Source: https://patents.google.com/patent/US8718021B2/en
Timestamp: 2019-12-09 21:01:42
Document Index: 791514249

Matched Legal Cases: ['§1', 'application No. 61', 'application No. 61', '§1', 'application No. 61', 'application No. 61', 'art 16']

US8718021B2 - Uplink control signal design for wireless system - Google Patents
Uplink control signal design for wireless system Download PDF
US8718021B2
US8718021B2 US12/830,959 US83095910A US8718021B2 US 8718021 B2 US8718021 B2 US 8718021B2 US 83095910 A US83095910 A US 83095910A US 8718021 B2 US8718021 B2 US 8718021B2
US12/830,959
US20110122846A1 (en
2008-07-07 Priority to US7858108P priority Critical
2009-07-03 Priority to US12/806,181 priority patent/US20110149846A1/en
2010-07-06 Priority to US12/830,959 priority patent/US8718021B2/en
2011-02-15 Assigned to NORTEL NETWORKS LIMITED reassignment NORTEL NETWORKS LIMITED ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: YUAN, JUN, NOVAK, ROBERT, VRZIC, SOPHIE, NIKOPOURDEILAMI, HOSEIN, YU, DONG-SHENG, FONG, MO-HAN
2011-05-26 Publication of US20110122846A1 publication Critical patent/US20110122846A1/en
2014-05-06 Publication of US8718021B2 publication Critical patent/US8718021B2/en
Transmission of uplink control message for a wireless system. The uplink control message may be encoded according to one of multiple possible schemes. The choice of encoding scheme may be made based on the control message size and/or based on the available transmission resources and/or based on the detection scheme used on the receiving end. A modulation scheme may also be selected based on such factors. CDM may be used for certain control messages. Block code encoding, such as Reed-Muller encoding may be used for certain control messages. Different transmission resources may be allocated for different control message uses. The encoding specifics may be selected to obtain a certain hamming distance and/or size of the encoded message or based on other factors.
This application is a continuation-in-part of the non-provisional application Ser. No. 12/806,181 resulting from conversion under 37 C.F.R. §1.53(c)(3) of U.S. provisional patent application No. 61/222,981 filed on Jul. 3, 2009, and which claims the benefit of U.S. provisional patent application No. 61/078,581 filed on Jul. 7, 2008.
This application is a continuation-in-part of the non-provisional application (serial number tbd) resulting from conversion under 37 C.F.R. §1.53(c)(3) of U.S. provisional patent application No. 61/222,981 filed on Jul. 3, 2009, which claims the benefit of U.S. provisional patent application No. 61/078,581 filed on Jul. 7, 2008.
This application relates to wireless communication techniques in general, and more specifically to control signaling in wireless communication and more specifically still to uplink control signaling.
A known approach for efficiently delivering high speed data over a channel is by using Orthogonal Frequency Division Multiplexing (OFDM). The high-speed data signals are divided into tens or hundreds of lower speed signals that are transmitted in parallel over respective frequencies within a radio frequency (RF) signal that are known as sub-carrier frequencies (“sub-carriers”). The frequency spectra of the sub-carriers overlap so that the spacing between them is minimized. The sub-carriers are also orthogonal to each other so that they are statistically independent and do not create crosstalk or otherwise interfere with each other. As a result, the channel bandwidth is used much more efficiently than in conventional single carrier transmission schemes such as AM/FM (amplitude or frequency modulation).
In wireless communication systems, control signals are used to pass information between sender and receiver for allowing the transmission of data therebetween. Control signals are not part of the transmission data being sent between users, but rather serve to coordinate communications between the sending and receiving devices, and otherwise to enable and facilitate communication. Generally, control signals are relatively important to communications, and they are usually transmitted in a more robust fashion than other data. While reliability of transmission of control signals is usually important, control signals are often quite small, despite their important role.
It is a basic objective in wireless systems to reliably transmit small quantities of information such as are found in control signals in a manner that function for all user scenarios. This represents a particular challenge in new standards such as IEEE802.16m, which aim to provide even more flexible deployment environment and support a variety of channel conditions, mobile speeds and other factors.
In IEEE802.16m, uplink control signals currently use sub-optimal modulation and coding schemes, in particular for the channel quality information channel (CQICH) and for acknowledgements (ACK). For example, a high overhead is imposed by the use of pilot in manners that have not been shown to be advantageous over other methods.
Accordingly, there is a need for an improved uplink control design for the mobile, broadband wireless access systems.
In accordance with a first broad aspect is provided a method for execution by a subscriber station for transmitting an uplink control message to a base station. The method comprises determining a size of the uplink control message. The method further comprises selecting an encoding scheme on the basis of the size of the uplink control message. The method further comprises encoding the uplink control message according to the selected encoding scheme to obtain an encoded uplink control message. The method further comprises modulating the encoded uplink control message according to a modulation scheme to obtain a modulated uplink control message. The method further comprises transmitting the modulated uplink control message uplink to the base station over a wireless interface. Selecting an encoding scheme comprises selecting a first encoding scheme being a code division multiplexing scheme if the size of the uplink control message is within a first size range, and selecting a second encoding scheme being a block code scheme if the size of the control message is within a second size range above the first size range.
In accordance with a second broad aspect is provided a method of transmitting an uplink control signal. The method comprises identifying encoding specifics having at least one selection criterion, each of the encoding specific in the set of encoding specifics having a respective minimum hamming distance associated with each of the encoding specific in the set of encoding specifics. The method further comprises selecting a set of encoding specifics to use in encoding at least in part on the basis of the hamming distance of the encoding specifics. The method further comprises choosing one of the selected encoding specifics, and encoding the uplink control signal in accordance with the chosen encoding specifics to obtain an encoded uplink control signal. The method further comprises modulating the encoded uplink control signal according to a modulating scheme to obtain a modulated uplink control signal. The method further comprises transmitting the modulated uplink control message uplink to the base station over a wireless interface.
In accordance with a third broad aspect is provided a method of communicating with a subscriber station. The method comprises allocating a first set of transmission resources to be used as a first uplink control transmission resource, the first uplink control transmission resource being shared by the subscriber station with a plurality of remote subscriber stations. The method further comprises allocating a second set of transmission resources to be used as a second uplink control transmission resource, the second uplink control transmission resource being an uplink control channel to be used by the subscriber station. The method further comprises communicating to the subscriber station the allocations of the first set of transmission resources and the second set of transmission resources. The method further comprises listening for transmission by the subscriber station of uplink control signals on at least one of the first and second set of transmission resources.
FIG. 4 is a block diagram of an example relay station that might be used to to implement some embodiments of the present application;
Referring to the drawings, FIG. 1 shows a base station controller (BSC) 10 which controls wireless communications within multiple cells 12, which cells are served by corresponding base stations (BS) 14. In some configurations, each cell is further divided into multiple sectors 13 or zones (not shown). In general, each BS 14 facilitates communications using OFDM with subscriber stations (SS) 16 which can be any entity capable of communicating with the base station, and may include mobile and/or wireless terminals or fixed terminals, which are within the cell 12 associated with the corresponding BS 14. If SSs 16 moves in relation to the BSs 14, this movement results in significant fluctuation in channel conditions. As illustrated, the BSs 14 and SSs 16 may include multiple antennas to provide spatial diversity for communications. In some configurations, relay stations 15 may assist in communications between BSs 14 and wireless terminals 16. SS 16 can be handed off 18 from any cell 12, sector 13, zone (not shown), BS 14 or relay 15 to an other cell 12, sector 13, zone (not shown), BS 14 or relay 15. In some configurations, BSs 14 communicate with each and with another network (such as a core network or the Internet, both not shown) over a backhaul network 11. In some configurations, a base station controller 10 is not needed.
OFDM modulation utilizes the performance of an Inverse Fast Fourier Transform (IFFT) on the information to be transmitted. For demodulation, the performance of a Fast Fourier Transform (FFT) on the received signal recovers the transmitted information. In practice, the IFFT and FFT are provided by digital signal processing carrying out an Inverse Discrete Fourier Transform (IDFT) and Discrete Fourier Transform (DFT), respectively. Accordingly, the characterizing feature of OFDM modulation is that orthogonal subcarriers are generated for multiple bands within a transmission channel. The modulated signals are digital signals having a relatively low transmission rate and capable of staying within their respective bands. The individual subcarrier are not modulated directly by the digital signals. Instead, all subcarrier are modulated at once by IFFT processing.
In operation, OFDM is preferably used for at least downlink transmission from the BSs 14 to the SSs 16. Each BS 14 is equipped with “n” transmit antennas 28 (n>=1), and each SS 16 is equipped with “m” receive antennas 40 (m>=1). Notably, the respective antennas can be used for reception and transmission using appropriate duplexers or switches and are so labelled only for clarity.
Reference is now made to FIG. 6 to illustrate reception of the transmitted signals by a SS 16, either directly from BS 14 or with the assistance of relay 15. Upon arrival of the transmitted signals at each of the antennas 40 of the SS 16, the respective signals are demodulated and amplified by corresponding RF circuitry 70. For the sake of conciseness and clarity, only one of the two receive paths is described and illustrated in detail. Analog-to-digital (A/D) converter and down-conversion circuitry 72 digitizes and downconverts the analog signal for digital processing. The resultant digitized signal may be used by automatic gain control circuitry (AGC) 74 to control the gain of the amplifiers in the RF circuitry 70 based on the received signal level. Initially, the digitized signal is provided to synchronization logic 76, which includes coarse synchronization logic 78, which buffers several OFDM symbols and calculates an auto-correlation between the two successive OFDM symbols. A resultant time index corresponding to the maximum of the correlation result determines a fine synchronization search window, which is used by fine synchronization logic 80 to determine a precise framing starting position based on the headers. The output of the fine synchronization logic 80 facilitates frame acquisition by frame alignment logic 84. Proper framing alignment is important so that subsequent FFT processing provides an accurate conversion from the time domain to the frequency domain. The fine synchronization algorithm is based on the correlation between the received pilot signals carried by the headers and a local copy of the known pilot data.
Once frame alignment acquisition occurs, the prefix of the OFDM symbol is removed with prefix removal logic 86 and resultant samples are sent to frequency offset correction logic 88, which compensates for the system frequency offset caused by the unmatched local oscillators in the transmitter and the receiver. Preferably, the synchronization logic 76 includes frequency offset and clock estimation logic 82, which is based on the headers to help estimate such effects on the transmitted signal and provide those estimations to the correction logic 88 to properly process OFDM symbols.
ASN-CSN tunneling.
ASN-CSN tunneling support;
Inter-CSN tunneling for roaming;
The Multi-carrier (MC) block enables a common MAC entity to control a PHY spanning over multiple frequency channels. The channels may be of different bandwidths (e.g. 5, 10 and 20 MHz), be on contiguous or non-contiguous frequency bands. The channels may be of the same or different duplexing modes, e.g. FDD, TDD, or a mix of bidirectional and broadcast only carriers. For contiguous frequency channels, the overlapped guard sub-carriers are aligned in frequency domain in order to be used for data transmission.
The Data Forwarding block performs forwarding functions when RSs are present on the path between BS and MS. The Data Forwarding block may cooperate with other blocks such as Scheduling and Resource Multiplexing to block and MAC PDU formation block.
Reference is now made to FIG. 12, which shows the CPS control, plane signaling flow and processing at the BS 16 and the MS 14. On the transmit side, the dashed arrows show the flow of control plane signaling from the control plane functions to the data plane functions and the processing of the control plane signaling by the data plane functions to form the corresponding MAC signaling (e.g. MAC management messages, MAC header/sub-header) to be transmitted over the air. On the receive side, the dashed arrows show the processing of the received over-the-air MAC signaling by the data plane functions and the reception of the corresponding control plane signaling by the control plane functions. The solid arrows show the control primitives among the CPS functions and between the CPS and PHY that are related to the processing of control plane signaling. The solid arrows between M_SAP/C_SAP and MAC functional blocks show the control and management primitives to/from Network Control and Management System (NCMS). The primitives to/from M_SAP/C_SAP define the network involved functionalities such as inter-BS interference management, inter/intra RAT mobility management, etc, and management related functionalities such as location management, system configuration etc.
Control signals, like other data, are transmitted over the wireless medium between the BS 14 and an SS 16 using a particular modulation scheme according to which the data is converted into symbols. Modulation of control messages will be described below in more detail, but for now, it should be noted that a symbol is the smallest quantum of information that is transmitted at once. A symbol may represent any number of bits, depending on the modulation scheme used, but commonly represents between 1 and 64 bits, and in some common modulation scheme, each symbol represents 2 bits.
In accordance with OFDM, the frequency spectrum is divided into a number of subcarriers. Individual subcarriers are used to transmit individual symbols. A subcarrier can thus be regarded as the smallest quantum of frequency resource which carries data. In terms of time, time can be regarded as being divided into slots of time of the duration required for transmitting a single symbol. These symbol-times (STs), can be regarded as the smallest quantum of time resource which can carry data.
Regardless of the modulation scheme used, a single modulated symbol is sent over a single subcarrier and generally represents the smallest quantum of information that can be sent over the air interface. Thus, as shown in FIG. 14, the total available transmission resources on which information can be transmitted can be represented as a two dimensional matrix 1400, wherein one dimension represents frequency (shown as axis 1405) and comprises every subcarrier 1415 and the other dimension represents time (shown as axis 1410) and comprises STs 1420. As such, transmission resources can be divided into blocks 1425 of subcarriers by symbols, where the subcarriers represents frequency resources and symbols represent time resources. These blocks 1425 each represent transmission resources capable of transmitting one single symbol.
Allocation of transmission resources for various purposes and entities will be illustrated herein using this matrix format. Transmissions may be described as occupying certain locations in the grid, such as certain areas within a frame (described in more details below). However it should be appreciated that the described and illustrated arrangements within the grid are logical in nature and are for illustrative purposes. The actual physical resources used for the purposes described herein may not be organized in the same manner as illustrated or described. In particular, a skilled person will appreciate that while blocks allocated for particular purposes may be shown herein as contiguous, the actual physical resources allocated may be non-contiguously spread across the frequency spectrum and across time according to a mapping for example to take advantage of frequency and/or time diversity.
As is well known in the art, the total available transmission resources illustrated in the grid 1400 may be allocated for different purposes and/or transmitting entities (e.g. BS 14 or individual SSs 16). It will be appreciated that the allocation of various portions of the total available transmission resources is done on the base station end and the allocation decisions are communicated to the SS 16. Furthermore, while transmission resources are shown as being allocated in contiguous blocks, when they are mapped onto actual physical resources, they may be spread out in such a way as to take advantage of frequency and/or time diversity.
FIG. 15 illustrates an exemplary frame 1500 in an OFDMA system. In this example, the frame 1500 is divided into subframes. More specifically, the frame 1500 is divided into a downlink (DL) subframe 1505 and an uplink (UL) subframe 1510. In the example shown, the system employs time division duplexing (TDD), whereby DL and UL transmissions are not sent simultaneously but rather are organized such that they occupy different places in time. Accordingly, the DL subframe 1505 and the UL subframe 1510 each occupy different and non-overlapping time segments.
The DL subframe 1505 contains DL bursts 1515 which contain respective DL transmission data payloads. The DL transmission data in the DL bursts 1515 may each be directed to different SSs 16, although several bursts may also be directed to a same SS 16.
The DL subframe 1505 also comprises a DL-MAP 1520 section which defines access to the DL information. The DL-MAP 1520 is a medium access control layer (MAC) message that defines burst start times for both time division multiplex and time division multiple access (TDMA) by a subscriber station (SS) on the downlink (DL). Among the information contained in the DL-MAP 1520, there may be a description of where among the physical transmission resources the contents of the DL subframe 1505 are located. Control over the UL transmission belongs to the BS, and the DL subframe also comprises a UL MAP 1525 portion contained as a first DL burst.
As shown, the frame 1505 comprises a preamble 1530, provided in the first subframe 1505. The preamble 1530 may be used to provide base station identification and selection, CIR measurements, framing and timing synchronization, frequency synchronization as well as channel estimation.
Within a sub-frame different types of control messages can be assigned to an SS 16 for transmission. The SS 16, may combine and jointly encode these control messages. An SS 16 is assigned different amounts of transmission resources for uplink control with different periodicity. For example, an SS 16 may receive X uplink control transmission resources every N sub-frames as well as Y uplink control transmission resources every M sub-frames. Should the periods N and M cause an occurrence of both these intervals at within a same sub-frame, the SS 16 may jointly encode the information that goes in X and Y or separately encode it.
The UL subframe 1510 comprises UL bursts 1540 which contain respective UL transmission data payloads. Each UL burst 1540 may originate from a different SS 16, although there may also be several UL bursts originating from a same SS 16. The UL subframe may also comprise a ranging subchannel which may be used for contention-based bandwidth requests.
It should be understood that other duplexing schemes may be used, such as frequency division duplexing (FDD). FIG. 16 shows a simplified illustration of a frame 1600 under a FDD duplexing scheme. As shown, under FDD, the DL and UL transmissions occupy different portions of the frequency resources, rather than time resources.
In a wireless transmission system such as the one described herein, control signaling is necessary to achieve proper transmission of transmission data. Control messages refers not to the actual transmission signals representing information that is intended to go from one user to another, but rather to other information, shared between two communicating wireless communication apparatuses to permit or facilitate transmission of the transmission signals. Control messages may include instructions through which the BS 14 instructs SSs 16 to do certain things, such as to transmit on certain resources, or to adopt certain modulation schemes. Control messages may also be more informational/feedback type signals. For example, channel quality indicator (CQI) signals may be sent to the BS 14 from an SS 16, which provide information on or related to the quality of a channel. Control messages may also include ACK/NACK messages, other responses to other signals, or even requests, such as bandwidth requests. In general, it is desired for control messages to be transmitted as reliably as possible since the proper transmission of all transmission data depends on the proper functioning of control messaging. The bit rate, on the other hand, tends to be of lesser concern for control messages, since they may represent a relatively small quantity of data and since the emphasis is rather placed on robustness.
Unless specified otherwise, control messages and signaling described herein refers to uplink control messages and signaling, although a skilled person will recognize, where applicable, the applicability of concept described herein to the downlink direction as well.
In general, control messages may have a variety of sizes. Small messages, such as ACK or NACK can have a bitlength of as few as 1 or 2 bits. CQI and other control messages may be medium sized. They may have a bit length of more than 2 and less than 70 bits, and CQI may have a bitlength in the neighborhood of 3-18 bits. Some control messages are larger and may have as much as 70-80 or more bits. It should be noted that the sizes of small, medium and large messages provided here are exemplary only. Other size ranges are possible for small, medium and large messages. Furthermore, while three message size ranges are provided here, fewer or more ranges are possible. For example, it may be possible to consider only small (e.g. 1-2 bits) and large (e.g. 3 or more bits) messages, or to consider small (e.g. 1-3 bits), medium (e.g. 3-70 bits), large (e.g. 70-80 bits) and extra large (over 80 bits) message sizes. It will be appreciated that other ranges/divisions are possible as well.
A sending SS 16 may determine a size of a control message in a number of ways. For example, it may simply know the size of the control signal by virtue of having generated it. Alternatively, it may determine the size of a control signal after it has been generated, either by measuring the size of the control message or by deducing its size, e.g. on the basis of the type of control message it is. For example, SS 16, may know that CQI messages always have a certain size, or always are within a certain size range. Also, SS 16 may have a default mode whereby control messages are assumed to be a certain size or within a certain size range, and it may determine the size of control messages to be transmitted
To avoid confusion, different terms will generally be used herein to describe data in the form of control messages, and the rest of the data being transferred using the wireless interface. Unless the context suggests otherwise, the terms control message data as used herein generally designate data that makes up control message, while the terms transmission data as used herein generally designate non-control data intended to be transferred over the wireless medium by some user (e.g. software or human) and may includes data packets with headers and payload.
A channel quality indicator (CQI) signal is a signal that provides information on the quality of a channel or information based upon which some knowledge of the quality of a channel can be inferred. In an example of CQI, an SS may send the BS one or more CQI associated with the SS, to provide the BS information based upon which certain aspects of the quality of the channel, e.g. as perceived by the SS, may be inferred.
Control channels may be allocated for the transfer of control messages. For example, the CQI may be sent in a channel quality indicator channel (CQICH). A control channel may be allocated to a specific SS or, may be allocated for use by more than one SS. CQI signals may vary in length or be of fixed length, in either case, a CQI signal may have any number of bits, for example, a CQI signal may be only a few bits long.
Acknowledge signals (ACK) are signals that can be used to acknowledge that something, such as a transmission, has taken place, or to indicate that something has been correctly received. ACK signals may be very short, and can have as few as one or two bits. ACK signals may be used, for example, when automatic repeat request (ARQ) or hybrid automatic repeat request (HARQ) methods are used. Under ARQ, an original transmitter transmits an original transmission to a recipient. If the original transmission is received correctly by the recipient, the recipient acknowledges this using an ACK signal. The original transmitter awaits receipt of an acknowledgement, and if a timeout occurs, that is, if an acknowledgement is not received within a specified period of time, the original transmitter may take further steps to ensure that the original transmission gets properly transmitted. For example, in the event of a timeout, the original transmitter may re-send the original transmission. In ARQ error-detection (ED) bits may be added to the original transmission to enable the recipient to determine whether there was an error in the original transmission. If an error is found, a negative acknowledge (NACK) signal may be returned to the original transmitter, indicating that the original transmission was not properly received. Under HARQ, forward error correction (FEC) bits may sometimes or always be added to the original transmission along with, or instead of, the ED bits such that the recipient can attempt to reconstruct the original transmission if an error occurred during its transmission. FEC bits are not necessarily added to every single transmission.
Fast-feedback, generally designates control messages that are time-sensitive. Fast-feedback messages may be physical layer-related messages that require a fast response. They are typically relatively short (in some examples there may be 3-6 such messages per slot) and are generally assigned their own transmission resources, such as slots.
The blocks 1425 of transmission resources can be organized in various ways. FIG. 17 shows an exemplary organizational of certain blocks 1425 used in the transmission of control messages, in this case UL control messages, are organized into tiles called control tiles 1705. The control tiles 1705 can have any of a number of dimensions, however, a size of 6 subcarriers by 3 STs (for a total of 18 blocks 1425) is shown here, which will suit well the encoding and modulating schemes suggested herein. As shown a block 1425 on each of two opposite corners of each control tile 1705 is reserved for a pilot signal, if pilots are used, or a null signal, if no pilots are used. (Despite the presence of “null” signals, it is considered in this case that no pilot signals are used/provided in the control tile 1705.) The other blocks 1425 may be used to transmit control message data. As such, up to 16 symbols (6×3 blocks−2 pilot signals) can be transmitted on every tile.
Control tiles 1705 do not need to have a constant location in every subframe. They may hop within a subframe. Control tiles 1705 may change frequency and/or time location from one subframe to the next, such that they do not always appear in the same position. As such, if a certain location of the available transmission resources is exposed to deleterious effects, control tiles 1705 will not suffer from these at every subframe.
Also as shown in FIG. 17, control tiles 1705 may be organized into resource units called here control resource units (RUs) 1710. Control RUs 1710 are allocated for uplink control message transmission. As shown, there may be 6 control tiles 1705 per control RU 1710 with each control RU 1710 having a dimension of 18 subcarrier by 6 STs. The control RUs 1710 may be shared by all SS 16 in the sector and may be distributed, e.g. in frequency and/or time, for diversity.
Control messages may be transmitted over control tiles 1705, but they may take up more than one control tile 1705. To this end, control channels are allocated, containing a number of control tiles 1705. Control channels may consist of 2, 4, 6, or 8 tiles, for example, which may be distributed over different control RUs 1710. This distribution may result in greater time/frequency diversity. A control message originating from an SS 16 may be allocated one matching control channel such that the encoded and modulated control message fits within the control channel. For example, a CQI signal may be transmitted in a CQICH channel which may be composed of, e.g. 4 tiles. This may be particularly true of medium sized control messages described above, although other sized control messages could also be allocated a matching control channel as well. The size of the control channel allocated will then depend upon the bit length of the control message, and the coding scheme and rate. Encoding and modulation of control message is discussed in more detail further below.
It is to be understood that not all control messages need be sent over a single respective control channel. Small control messages, for example, such as 1 or two bit ACK/NACK messages, may be multiplexed together from several SSs 16 onto a same control tile 1705. Large control messages, on the other hand may be transmitted using transmission resources other than the control channels/control tiles 1705/control RUs 1710 described above. For example, large control messages may be transmitted with user data/transmission data.
The overall amount of transmission resources that is employed to transmit a control message depends upon the bitlength of the control message, but also upon the encoding scheme with which it is encoded.
The number of bits that can be transmitted in each tile depends upon the modulation scheme used, since this has an effect on the number of bits that each symbol in each block 1425 in the tile represents. The manner in which data is mapped onto symbol depends upon the modulation scheme utilized. In phase-shift keying (PSK), symbols are usually represented as a certain phase shift imparted on a reference signal. In one example of PSK, quadrature phase-shift keying (QPSK), four symbols are usually represented as four points in a constellation diagram representing different phase shifts imparted on the reference signal. Since there are four possible symbols, each symbol represents two bits of data. In contrast, binary phase-shift keying (BPSK) represents symbols as only one of two possible phase shifts and thus each symbol represents a single bit (one of two possibilities). Higher-order PSK is achievable by providing a constellation having more points (representing different phase-shifts and amplitudes), however as the number of points in the constellation increase, the error-rate tends to increase as well. Modulation such as higher order quadrature amplitude modulation (QAM) tend to be used to provide a greater number of possible symbols. For example, on high quality channels, 64-QAM, which provides 64 different symbols, can be used, wherein each symbol represents 6 bits.
Thus it will be appreciated that the number of bits that can be transmitted in one control tile 1705 depends on the number of bits that each of the 16 blocks 1425 used for transmission data in the control tile 1705 represents. For example, if BPSK is used, each symbol represents one bit, and a total of 16 bits can be carried in the tile. If, on the other hand, QPSK is used, each symbol represents 2 bits, and thus as much as 32 bits of data can be transmitted on the tile.
In regular PSK, symbols are generally represented as a certain value of phase shift. For example, in QPSK, “11” may be represented as a 45 degree phase shift, “01” as a 135 degree phase shift, “00” as a 225 degree phase shift, and “10” as a 315 degree phase shift. However, effects in the communication channel can cause the constellation to be rotated over time. As such, a pilot signal which provides a reference phase is commonly used with regular PSK.
In order to minimize potential error, gray coding may be used with PSK methods, whereby adjacent symbols represent values differing only by one bit. Assuming that an error is more likely to cause a symbol to be misread as another symbol that is nearby in the constellation, rather than far away, gray mapping reduces the number of erroneous bits resulting from such an error.
As an example, if QPSK is used to modulate an encoded control message, every two coded bits are mapped to one QPSK symbol (using gray mapping) and 16 QPSK symbols are mapped to one control tile 1705.
Differential phase-shift keying (DPSK) overcomes the problem of constellation rotation by defining symbols as a change in phase rather than a particular phase. An increase or decrease of the current phase by a certain angle value may therefore represent a certain symbol. Thus if an effect in the communication channel causes the phase of the signal to shift gradually over time, this may not affect symbol detection if the shift is significantly smaller, within the time frame of a signal than the shifts indicative of a symbol. Even if an effect causes an instant, significant shift of the signal, this will only result in a single symbol being misread, since the next symbol will be represented as a particular change in phase from whatever the previous phase is.
The term “previous” phase here is not intended to be necessarily chronological. That is, the changes in phase for DPSK may be implemented over time or frequency or both. FIGS. 19A and 19B illustrate two examples. The arrows represent the path along which each block 1425 carries a symbol defined by the difference in phase between that block and the previous block along the arrow's path. In FIG. 19A, time directed DPSK, the modulating phase differences cross time barriers first while in FIG. 19B, frequency directed DPSK, the modulating phase differences cross frequency subcarriers first.
As an example of DPSK modulation, if pi is a QPSK symbol, then a DPSK symbol, zi is defined as shown in formula (1):
z i =z i-1 p i (1)
FIG. 18A shows a control tile 1705 which comprises two pilot signals 1805, as described above. If non-coherent detection is to be used for detecting the control message transmitted on a control tile 1705, then the two pilot signals may be omitted and replaced by null signals 1810, as shown in FIG. 18B. The null signals 1810 represent a subcarrier which is not driven at all. Since no power is used for pilot subcarriers (which are otherwise often provided even greater power than the other subcarriers), the total power available for the control tile can be spread uniquely among the blocks 1425 control message symbols, allowing a greater signal power for the resources transmitting control message symbols than if pilot signals are used.
Prior to modulation, control messages are encoded to add redundancy for error detection and/or correction. A single encoding scheme may be used for a subset or all of the control messages. However, in this example, a particular encoding scheme is selected based on the size of the control message to be transmitted. In particular, small control messages, for example, such as 1 or two bit ACK/NACK messages, may be code division multiplexed (CDM) using spreading sequences. There are several options for spreading sequences, including DFT spreading, Walsh codes and CAZAC). A single option may be used for all small control messages, or a decision logic may select a particular option based on the circumstances and/or data to be transmitted and/or transmission resources.
With CDM several small control messages may be transmitted over a same transmission resource. In particular, several small control messages may be transmitted over a same control tile or control RU. For added robustness, repetition may be used, whereby transmitted data is transmitted multiple times. Repetition may be tile-based, rather than bitwise, such that entire tiles, not individual bits, are repeated.
Small control messages that are code division multiplexed may originate from different SSs 16. Thus multiple users may use a same shared resource such as a same control tile 1705 or control RU 1710. Alternatively, sharing may be limited to control messages originated from a same SS 16 and code division multiplexed signals using a shared transmission resource (e.g. a control tile 1705) may all originate from a same SS 16.
For medium control messages, such as control messages having less than 70 bits, or control messages having between 3 and 18 bits, another scheme may be used. These control messages, which may be for example CQI messages, may be encoded using a block code encoding scheme such as Reed-Muller (RM) encoding. RM encoding benefits from low complexity and has a fast decoding algorithm. Although fast decoding algorithm may be utilized, it should be noted that any suitable decoding algorithm may be used. RM encoding is optimal for small to medium messages with a block length of less than 32 bits. As used herein, the term codeword refers to an encoded message and block length refers to the bitlength of the codewords generated by the encoding scheme. The term block length is not related to the blocks 1425 which represent transmission resources for transmitting one symbol.
For a given RM code, the block length is denoted as n, and the maximum number of bits that can be encoded is denoted as k. In general, n will be greater than k. As such, for a given RM code, not all combinations of n bits represent valid codewords since not all combinations of n bits could have been generated by the RM code with an input of k bits. Stated differently, there are 2k different possible strings of k 1's and 0's which, when encoded result in 2k different possible valid codewords. However, there are 2n different possible strings of n 1's and 0's and 2n>2k, it therefore follows that certain combinations of n 1's and 0's cannot be the result of the encoding of a k bit input, and therefore are not valid codewords, since they don't stem from they couldn't have been generated by the RM code.
The set of all valid codewords may be called the codebook, and is designated P. An individual codeword from the codebook P is designated p. For control messages being transmitted through a control channel, which, as described above, may be made up of a number of control tiles, we say that p=[pij] where pij represents one QPSK symbol at block 1425 j of tile i, where i=1, . . . , l (l being the number of tiles in the control channel, such as 2, 4, 6 or 8, for example) and j=1, . . . , 16 (since there are 16 blocks 1425 in the exemplary tile used here).
When encoding a message, it is generally desired to produce encoded blocks having a high minimum hamming distance. The hamming distance refers to the number of bits that must be flipped to go from one valid codeword to another encoded block which corresponds to a different encoded message. The minimum hamming distance, designated dmin herein, refers to the smallest of all the hamming distances for a set of valid codewords. For Example, for a codebook made up of two codewords “000000” and “111111”, the minimum hamming distance is 6, since all 6 bits of one valid code need to be flipped to obtain the other valid code. If, however, we were to add the codeword “001111” in our codebook, the minimum hamming distance would drop down to 2, since there exist one valid codeword for which only 2 bits need to be flipped to obtain another valid codeword (specifically, flipping the first two bits of “001111” gives “11111”, another valid codeword).
Repetition involves deliberately repeating transmitted bits to increase reliability of a transmission. Repetition is often done on a bitwise basis. For example, a word “101” with three repetitions might become “111000111”. In the present example, repetition is tile-based, meaning that entire tiles are repeated. The tiles may be repeated intact such that repeat tiles have the same contents as the original tile of which they are a repeat. In general, R repetitions increases dmin by a factor of R. Thus a codebook P that features a minimum hamming distance, dmin, of 8, will have a dmin of 32 if 4 repetitions, R, are employed.
A given RM code is given as RM(m, r) where m and r are parameters of the RM code. Parameter m is determinative of the block length n resulting in the encoding, the relationship between m and n being given as shown in formulae (2) and (3):
m=log2(n) (2)
n=2m (3)
Parameter r is the code order. For example, RM codes with order r=0, RM(m, 0) are mere repetition codes with the data repeated 2m times (k=1). RM codes with order r=m−1 provide a parity bit. R(m, m−2) gives a hamming code.
The maximum number of bits k that can be encoded with a given RM code is defined by formula (4):
k = ∑ i = 0 r ⁢ ( m i ) ( 4 )
The value k is also the largest control message (in bitlength) that can be encoded using a particular RM code. As will be appreciated, the parameters m and r define the maximum length of a control message that can be encoded by a certain code. Thus the particular code used for a control message may be selected in part based on the size of the control message to encode.
Turning back to FIG. 17, if RM(6, 1) (which means n=64; k=7) and R=1 is used alongside QPSK or DPSK (two bits per symbol), the two control tiles 1705 shown can hold one control message that is 7 bits long before encoding. The encoded message takes the form of a 64 bit codeword which fits exactly into the 32 block 1425 contained by the two control tiles 1705.
The minimum hamming distance dmin for a codebook P corresponding to an RM code RM(m, r) depends upon the parameters m and r. It is given by formula (5):
d min=2m-r (5)
Keeping in mind that the presence of repetition affects the hamming distance, we get an overall hamming distance defined by formula (6):
d min=2m-r R (6)
If dmin bit errors occur in the transmission of one codeword, it is possible that the received data codeword will correspond exactly to another codeword. Thus the presence of an error may be undetected by the receiver, where it will seem that the incorrect error was received perfectly. On the other hand, any fewer bit errors are guaranteed not to result in the received codeword corresponding to a valid codeword. Therefore for any number of bit errors of less than or exactly to dmin−1 bits, the presence of an error can be detected.
When a codeword containing errors is received, the receiver, e.g. the BS 14, may choose to discard it, or it may choose to interpret it as the closest valid codeword. In the latter case, the receiver will correctly interpret the control message every time the number of bit errors do no cause the received codeword to resemble another codeword more closely than the correct codeword. In other words, any received codeword having fewer than (dmin/2)−1 bit errors will be correctly interpreted, essentially correcting the bit errors therein. The BS may also choose not to correct in this manner received codewords lying too close to the midpoint between two valid codewords, that is, received codewords appearing to have close to dmin/2 errors.
The code rate of a given RM code is given as the ratio of the bits encoded (which will be assumed here to be k) to the block length n. Repetitions increase hamming distance and reliability but reduce the code rate. If there are R repetitions, the code rate is reduced by a factor of R. Thus the overall code rate can be defined by formula (7):
m = k nR ( 7 )
Encoding specifics may refer to the specifics pertaining to a particular encoding. For example, the RM code itself that is used for an encoding would be considered an encoding specific, as would the parameters that define the code. Other encoding specifics include the repetitions numbers, and indeed anything that affect the end result of the encoding process.
The manner of selecting encoding specifics may be done as follows: First RM codes of a certain order or range of order are chosen. In this example, only RM codes of order r=1 or 2 will be selected. Then, codes with parameters providing a reasonable or desired block length n are chosen. The desired code order and the desired block length (or the value of m corresponding to the desired block length) can be viewed as first and second (or vice versa) selection criteria, only one of those two criteria may be used. In this example the first and second selection criteria define the parameters of the RM code. The desired block length n may be selected in part or wholly on the basis of tile size and subchannel size. For example, if subchannels of 2, 4, 6 and 8 tiles of 16 transmission blocks 1425 each are available, and if QPSK is used (2 bits per transmission block 1425), then it the parameter m may be selected in view of making the encoded data fit into 64 bits (2 tiles), 128 bits (4 tiles), 192 bits (6 tiles), or 256 bits (8 tiles). However, keeping in mind that repetitions might be used, the block length may be selected to be smaller than these numbers of bits by some repetition factor R. These codes may then be sorted by overall hamming distance.
FIG. 20 shows a table 2000 representing different RM codes on each row from among the RM codes chosen as described above. For each RM code, the table 2000 lists the value of the parameters and characteristics associated with each code. As can be seen, the code order r was set to 1 and 2 only, while the value m, was varied between values that result in a block length n of between 16 and 256. In addition to the values of r and m, that define the RM codes, different values of R, that is, different numbers of repetitions are also shown in the table. Values of k, n, k/n, hamming distance, overall code rate, overall hamming distance, and number of tiles required can be derived using the formulas and relationships described above. The rows in the table 2000 are grouped by overall hamming distance, and they are arranged within each group of overall hamming distance in increasing order of hamming distance without repetition.
From the selected RM codes listed in table 2000, a further selection can be made based on hamming distance. This represents a third selection criterion. As shown in this example, for each overall hamming distance, the RM code characterized by the highest individual hamming distance (that is, the value of that the minimum hamming distance would have, were there no repetitions) is selected. These selected RM codes 2005 are shown as boxed in table 2000.
FIG. 21 is a reduced table 2100 of RM codes similar to table 2000 but with only the selected RM codes 2005 removed. These selected RM codes 2005 may be used to encode control message data over control tiles 1705. The selected RM codes 2005 in the reduced table 2100 may be evaluated with different modulation and detection schemes with a view of selecting a specific RM code that will be used for a transmission. Alternatively, or additionally, the size in bits of the control message to be encoded or the available resources (e.g. number of control tiles 1705 in an available control channel or available control RUs 1710) may inform the decision of which of the selected RM code 2005 to use. Furthermore, the detection scheme used may also be taken into account when selecting an encoding. For example, selection may take into account whether detection will be coherent or incoherent.
In certain cases, slight adjustments will be necessary in order to reconcile slight differences in the size of the control data to transmit and/or available resources and the values of k and n for the available RM code(s). These adjustments can be made using RM sub-code or punctured codeword.
RM sub-codes may be used when the bits of control (or other) data to transmit are smaller than k, the number of bits that the RM code being used can handle. In such a case, it may be desirable not to use the entire codeword of n bits; rather it may be modified to use fewer bits. Assume that x bits are to be encoded and that x<k for the RM code being used. A subset of the 2k valid codewords in the codebook P of the RM code are selected. In particular 2x codewords are selected, one for each possible string of x bits. The subset of 2x codewords is selected such as to maximize the hamming distance between the codewords in the subset. Any manner of making such a selection may be used, for example, doing an exhaustive search of all the possible subsets will yield the optimal selection of codewords such that the subset has the highest possible minimum hamming distance. The receiver of the transmission knows the possible codewords.
The receiver may be made aware of the possible codewords in any suitable manner. For example, the BS 14 may communicate the selected codewords to the SS 16 using control signaling. Alternatively, other cues may indicate to the SS 16 which codewords are used, or may indicate to the SS 16 how to determine which codewords are used. For example, the SS 16 may be made aware of the size of the subset of codewords by any suitable manner, and may then proceed to performing the same process as done on the sending side to determine which codewords are in the subset. Alternatively still, certain subsets of codewords may have been agreed upon at an earlier time (e.g. for different sizes of subsets) or the SS 16 may itself select the codewords to use in the subset and provide these to the BS 14 in one or more control messages.
Using RM sub-codes may simplify the decoding, since fewer possible codewords are used, and in any event, the minimum hamming distance is improved, resulting in a more reliable transmission. However, RM sub-codes affect the code rate by lowering it a bit, since the ratio of encoded bits to codeword bits is lower (x/n is lower than k/n).
Puncturing is used when the block size n is too high for the available bandwidth. In this case, the goal is to reduce the size of the codewords, thereby increasing the code rate and reducing slightly the reliability of the transmission. Essentially, some bits are “punctured” out of each codeword (removed). This has the effect of reducing the length of the codewords, but it also reduces redundancy. The hamming distance is also likely to drop since with fewer bits in each codewords, less bit errors will be needed to go from one valid codeword to another. Any manner of puncturing codewords may be used, however it will be appreciated that using the pattern bits to puncture out may be selected according to some optimization so as to minimize the reduction in hamming distance. For instance, an exhaustive search of all the patterns may reveal which one yields the best results. It will be noted that in some cases, it may be decided to use full codeword length for utilizing fast decoding algorithms.
Using RM sub-coding and puncturing, it is possible to adapt control (or other) message for encoding using an RM code that is not ideally suited (in terms of associated k and n values) to the length of the control (or other) message and available transmission resources. A relatively small number of RM codes, such as the selected RM codes 2005 listed in the reduced table 2100, or even a single RM code may be used for a variety of different circumstances. In the case where a number of RM codes are available, the best match may be used and adaptation by RM sub-coding and/or puncturing may be used to adapt the code to the actual circumstances.
Adaptation using RM sub-coding or puncturing may be particularly useful when a message length changes. Control messages have types or formats that are pre-defined. They contain a message type field that indicates what is contained in the message. The SS 16 may dynamically change the contents of a fast feedback message by changing the message field type. This may incur a small change in the message length. Such small changes can be handled using the methods described above.
In an example of Reed-Muller coding, RM(5, 1) with 3 repetitions was proposed for a CQICH channel for WiMax. In that case, m=5, r=1 and R=3. This provides a minimum hamming distance of 48, translating to a 0.5−1 dB Signal to Noise Ration (SNR) gain. For this, two PUSC tiles are used per codeword, totaling 16 data tones or 32 bits with QPSK modulation. With the three repetitions, one slot of 6 PUSC tiles are used.
An example of Reed-Muller coding will now be provided in the context of UMTS. In this example, 6-10 bits of transport format combination indicator (TFCI) are coded using RM(6, 2). However, a RM sub-code was used to reduce the number of codewords to 10 codewords of 64 bits (26=64). Moreover, the sub-codes are punctured to have a block size of 48 bits. For 3-5 bits TFCI, RM(5,1) may be used with sub-codes to reduce the number of codewords to 5. Additionally, the reduced codewords are punctured to achieve a block size of 24 bits. For 1 or 2 bit long message, repetition codes are used.
Another example will be provided in the context of LTE, where RM codes are used for channel quality information feedback, which are messages of length greater than 2 bits. In this example, a sub-code yielding a 32 codewords of length 14 (derived from RM(5, 2)) is used for CQI/PMI transmitted in PUSCH. The sub-codes are then punctured to achieve a block size of 20.
In terms of multiplexing for medium sized control messages, frequency-division multiplexing may be employed on a control-tile basis.
Setting aside medium control messages now, larger control messages, such as control messages having 70-80 bits or more in length may be handled differently. For example, in terms of encoding, it has been stated that Reed-Muller code is an optimal channel coding option for small to medium message sizes. However, for larger control messages, convolutional codes or other encoding schemes may be a better option. In this example, selection of the encoding scheme may be based at least in part upon control (or other transmitted) message length. Rather than to occupy specific control channels made up of control tiles 1705, large packet control messages may be transmitted as data traffic e.g. in the same manner as transmission data is transmitted. Large signals may also be handled by requesting additional resources. For example, specific bandwidth requests may be issued to communicate large control messages.
If control resources are assigned to an SS 16, but the SS 16 has to send a control message that is too long for the amount of control resources that it is assigned, the MS may send the long control message with transmission data, if it has been assigned transmission resources for transmission data. For example, the control message may be sent in the form of a MAC layer protocol data unit with a header and no user data payload. Alternatively, in the above scenario, the SS 16 could select a fast feedback message that includes a request for additional control resources. This may result in the assignment of a fixed number of resources for a single transmission. In yet another alternative, the SS 16 may also send control signaling additional to that for which it has resources assigned by selecting a message type that contains a normal bandwidth request. In such a case the SS 16 may indicate the quantity of transmission resources required.
Turning now to the detection side, different detection schemes are possible. The signal and pilot design may depend on the detection scheme used. In particular, the particular detection scheme used may affect the bit error rate (BER), and thus affect the best choice of encoding/modulation used to achieve the necessary robustness for control signals. These may be classified into two broad classes, sequence detection and symbol-level detection.
In sequence detection, a soft detection is performed on the received sequence of symbols based on a probability, weight, and/or value of each (e.g. QPSK) symbol. Sequence detection requires that the receiver know the whole set of valid codewords. The receiver can do, for example, an exhaustive search over all the codewords. In one example, a weight is assigned for each received symbol and the weight is used to find the best match using probabilistic methods. Sequence detection may involve phase estimates, for which the receiver must be able to estimate the phase in order to have an idea of how good a given match is. Determining what codeword has been received may involve looking at the phase of the signal (e.g. at every ST) and to apply probabilistic logic to determine what codeword was received. Sequence detection occurs at the physical (PHY) level and provides physical level error detection. As such, there is no need for algebraic error detection.
In symbol-level detection, demodulation occurs symbol-by symbol and each symbol may be demodulated without regards to the other symbols that would make up a codeword. For each symbol, a decision is taken as to what symbol has been received. For this, there is no need to be able to estimate the phase, it is simply required that the receiver can take a decision as to which symbol it has received. Once a signal has been demodulated and is now in digital form, algebraic (e.g. Reed-Muller) decoding occurs in the digital domain. Error detection and correction (if applicable) are both algebraically applied. For this scheme, it is not necessary for the receiver to have the set of codewords.
Generally speaking, detection may also be classified into the two classes of coherent and non-coherent detection. In coherent detection, pilot signals are used to enable or facilitate deriving channel estimations. Coherent detection with a good channel estimation quality may be a good option for high code rate at high SNR.
In non-coherent detection, there are two options: pilot-assisted and non-pilot assisted. In non-pilot assisted non-coherent detection, null pilots may be transmitted in lieu of pilot signals. As mentioned above with reference to FIG. 18B, replacing pilot signals with null signals may leave more power available for the other blocks 1425 in a tile, and thus data tone power can be boosted for these blocks for increased detection. With non-coherent methods, there may be no need for channel estimation. Non-coherent detection may be a good option for low code rate and low SNR. Pilot-assisted non-coherent detection are non-coherent detection methods that make use of the pilot signals to derive an even more accurate detection.
In an example of Coherent Sequence Detection of a QPSK signal sent with two pilots using the control tiles described above, an estimated codeword is derived according to the formula (8):
p ^ = arg ⁢ ⁢ max p = [ p ij ] ∈ P ⁢ Re ⁢ { ∑ i , j , k ⁢ h ^ ijk * ⁢ p ij * ⁢ y ijk } ( 8 )
Here, yijk represents the received symbol at the receive antenna number k. The receiver might contain 1, 2, or 4 receiving antennas, for example at p represents the codework, {circumflex over (p)} is the received symbol. The other input, ĥijk, represents the estimated channel between the transmit antenna and the kth receive antenna of the receiver for the data tone j of tile i. The channel is estimated based the two pilot signals 1805 on each tile 1705 as received at the receiver. In one example, the two pilot signals may be averaged over the control tile. As can be seen, by the presence of pij in Formula (7), this sequence detection method requires knowledge of the codebook P.
With the above coherent sequence detection scheme, error detection may be defined according to formula (9):
Re ⁢ { ∑ i , j , k ⁢ h ^ ijk * ⁢ p ij * ⁢ y ijk } ⁢ | p ^ ∑ p = [ p ij ] ∈ P , p ≠ p ^ ⁢ Re ⁢ { ∑ i , j , k ⁢ h ^ ijk * ⁢ p ij * ⁢ y ijk } > Th ( 9 )
Sequence detection of a QPSK signal sent with two pilots using the control tiles described above can also be performed non-coherently. As mentioned above, and as will be clear from the below formula, there is no need for channel estimation according to this scheme. The formula (10) which defines non-coherent (pilotless) signal detection does not comprise a channel estimate input:
p ^ = arg ⁢ ⁢ max p = [ p ij ] ∈ P ⁢ ∑ i , k ⁢  ∑ j ⁢ p ij * ⁢ y ijk  2 ( 10 )
With pilot-assisted non-coherent sequence detection, information derived from the pilot signals can be used to derive an even more accurate detection, as shown in Formula (11) wherein tim represents pilot m of tile i.
p ^ = arg ⁢ ⁢ max p = [ p ij ] ∈ P ⁢ ∑ i , k ⁢  ∑ m = 1 , 2 ⁢ t im * ⁢ r imk + ∑ j ⁢ p ij * ⁢ y ijk  2 ( 11 )
In both the pilotless and pilot-assisted non-coherent sequence detection schemes shown here, knowledge of the codebook is required.
For non coherent detection as described here, error detection is defined according to Formula (12):
{ ∑ i , k ⁢  ∑ m = 1 , 2 ⁢ t im * ⁢ r imk + ∑ j ⁢ p ij * ⁢ y ijk  } ⁢ | p ^ ∑ p = [ p ij ] ∈ P , p ≠ p ^ ⁢ ∑ i , k ⁢  ∑ m = 1 , 2 ⁢ t im * ⁢ r imk + ∑ j ⁢ p ij * ⁢ y ijk  > Th ( 12 )
Here again, Th is a threshold, which, if surpassed, an error is considered to be detected in the detected codeword. If the threshold is not surpassed, and the above inequality formula holds true, then the detected codewords is considered valid.
So far the detection scheme that have been described have assumed QPSK demodulation. If DPSK demodulation is to be used, different formulas will apply, since the symbols are not demodulated in the same way. To begin with, DPSK demodulation employs differential phase detection. With differential phase detection, if yl is a received symbol corresponding to the DPSK symbol zi, then:
{tilde over (p)} i =y* i-1 y i ˜|h i|2 p i +n i (13)
After differential phase detection, either sequence detection may occur or symbol-level detection. If sequence detection is employed, codewords are derived according to formula (14):
p ^ = arg ⁢ ⁢ max p = [ p ij ] ∈ P ⁢ Re ⁢ { ∑ i , j , k ⁢ p ij * ⁢ p ~ ijk } ( 14 )
Error detection is additionally possible with this detector by setting a threshold on normalized correlation.
On the other hand, if symbol-level detection is employed, a first derepetition stage must be performed. Dereptition utilizes maximal-ratio combining (MRC) whereby replicated symbols are added together. For example, if {tilde over (p)}i and {tilde over (p)}j are two replicas of the same symbol, then these are added together:
{tilde over (p)} i +{tilde over (p)} j=(|h i|2 +|h j|2)p i +n i +n j (15)
After MRC, a hard decision is taken for every symbol as to what symbol they represent. Every complex symbol is thus demapped to 2 binary bits. Binary bits form the received binary word c=(c1,c2, . . . ). RM decoding is then applied. The c is then decoded to information bits, b and if the weight of detected error exceeds a given threshold, then b is considered invalid and an error is detected.
FIG. 22 illustrates a decision tree 2200 governing the determination of which detection scheme will be used.
First, at the root 2205, an encoding scheme is used to encode data to transmit. In this case, the encoding scheme is RM encoding as described above. Branches 2210 and 2215 illustrate whether the encoded data is modulated using DPSK or QPSK respectively.
Beginning with branch 2210, reference symbols are agreed upon or known to both sides of the transmission (recall z0) and differential demodulation, which utilizes the reference symbols takes place on the receiver end. After differential demodulation, there are two possible branches. Following branch 2220, the receiver performs sequence detection in the manner described above, and error correction/detection ensues.
If after differential demodulation branch 2225 is employed, this means that symbol-level detection will take place, as described above. Before symbol-level detection, as described, derepetition is first undertaken using MRC, which is then followed by the actual symbol-level detection. The logical data that results from the detection is then RM decoded.
Returning to the root, if the encoded message had been modulated using QPSK (branch 2215), two possibilities might be true of the resulting signal: either pilot signals are present, or null signals are present instead. If null signal are present (branch 2230), then pilotless non-coherent sequence detection must take place as described above. If, on the other hand pilot signals are present (branch 2235), it is still possible to perform pilotless non-coherent sequence detection, by ignoring the pilot signals (branch 2240). On the other hand, the presence of signals opens the possibility of performing pilot-assisted non-coherent sequence detection, in the manner described above. This is illustrated as branch 2545. Branch 2250 illustrates the option of performing coherent sequence detection, as described above, using the pilot signals to estimate the channel. Finally, shown in decision branch 2255, it is also possible to perform symbol-level detection by employing RM decoding on logical recovered data, rather than physical-level detection. For this derepetition/MRC combining must take place and symbol-level detection is informed by hard decisions as previously described. Finally RM decoding takes place on the hard-decided logic symbols detected.
Several open-loop MIMO schemes may be employed for the transmission of uplink control signal. These may include the application of code division duplexing (CCD) on a per-tile basis when using non-coherent detection or DPSK. CCD may be applied on a per-block 1425 basis if coherent detection is being used. Also, differential space-time codes (STC) may be used with non-coherent detection.
A method for execution by a subscriber station for transmitting an uplink control message to a base station will now be described with reference to the flow chart illustrated in FIG. 23. A first step 23-1 of the method involves determining a size of the uplink control message. A second step 23-2 involves selecting an encoding scheme on the basis of the size of the uplink control message, wherein the selecting an encoding scheme comprises selecting a first encoding scheme being a code division multiplexing scheme if the size of the uplink control message is within a first size range, and selecting a second encoding scheme being a block code scheme if the size of the control message is within a second size range above the first size range. A third step 23-3 of the method involves encoding the uplink control message according to the selected encoding scheme to obtain an encoded uplink control message. A fourth step 23-4 involves modulating the encoded uplink control message according to a modulation scheme to obtain a modulated uplink control message. A fifth step 23-5 involves transmitting the modulated uplink control message uplink to the base station over a wireless interface.
A method of transmitting an uplink control signal will now be described with reference to the flow chart illustrated in FIG. 24. A first step 24-1 of the method involves identifying encoding specifics having at least one selection criterion, each of the encoding specifics in the set of encoding specifics having a respective minimum hamming distance associated with each of the encoding specifics in the set of encoding specifics. A second step 24-2 involves selecting a set of encoding specifics to use in encoding at least in part on the basis of the hamming distance of the encoding specifics. A third step 24-3 of the method involves choosing one of the selected encoding specifics, and encoding the uplink control signal in accordance with the chosen encoding specifics to obtain an encoded uplink control signal. A fourth step 24-4 involves modulating the encoded uplink control signal according to a modulating scheme to obtain a modulated uplink control signal. A fifth step 24-5 involves transmitting the modulated uplink control message uplink to the base station over a wireless interface.
wherein the selecting an encoding scheme comprises selecting a first encoding scheme being a code division multiplexing scheme if the size of the uplink control message is within a first size range, and selecting a second encoding scheme being a block code scheme if the size of the control message is within a second size range above the first size range.
2. The method of claim 1, wherein selecting an encoding scheme further comprises selecting a third encoding scheme if size is within third size range above the second size range.
3. The method of claim 2, wherein the third encoding scheme is a convolutional code encoding scheme.
4. The method of claim 1, wherein the second encoding scheme is Reed-Muller encoding.
5. The method of claim 1, wherein transmitting the modulated uplink control message comprises transmitting the modulated uplink control message over a first transmission resource if the size of the uplink control message is within the first size range; and transmitting the modulated uplink control message over a second transmission resource if the size of the uplink control message is within the second size range.
6. The method of claim 5, wherein the first transmission resource is a shared transmission resource onto which at least one additional uplink control message is code division multiplexed.
7. The method of claim 6, wherein at least one of the at least one additional uplink control message originates from a remote subscriber station.
8. The method of claim 5, wherein the second transmission resource is a control channel comprising one or more control tiles from among a set of control tiles, the set of control tiles defining a portion of transmission resources dedicated to uplink control.
9. The method of claim 8, wherein the control channel is provided without pilot signal.
10. The method of claim 8, wherein each control tile in the control channel is allocated by the base station for use by the subscriber station to send an uplink control message.
11. The method of claim 10, wherein the uplink control message is a channel quality indicator message and the control channel is a channel quality indicator channel.
12. The method of claim 8, further comprising if the size of the uplink control signal is within the second range, selecting the encoding scheme at least in part to cause the encoded message to suit a quantity of transmission resources available in the control channel.
13. The method of claim 1, wherein the first size range is between one and two bits inclusively.
14. The method of claim 1, wherein the second size range is between two and seventy bits exclusively.
15. The method of claim 14, wherein the second size range is of 3 to 18 bits.
16. The method of claim 2, wherein the third size range begins at seventy bits.
17. The method of claim 1, wherein at least one of the selected encoding scheme and the modulation scheme is selected on the basis of a detection scheme employed at the base station.
18. The method of claim 1, wherein selecting an encoding scheme comprises determining whether to select an encoding scheme other than a default encoding scheme.
19. The method of claim 18, wherein the determining a size of the uplink control message comprises determining whether the uplink control message lies outside of a default size standard.
20. The method of claim 18, wherein the default encoding scheme is RM(6,2).
21. The method of claim 1, further comprising selecting the modulation scheme on the basis of the size of the uplink control message.
22. The method of claim 21, further comprising if the size of the uplink control signal is within the second range, selecting at least one of the encoding scheme and the modulation scheme at least in part to cause the encoded message to suit a quantity of transmission resources available in the control channel.
23. The method of claim 21, wherein at least one of the selected encoding scheme and the modulation scheme is selected on the basis of a detection scheme employed at the base station.
a. identifying encoding specifics having at least one selection criterion, each of the encoding specifics in the set of encoding specifics having a respective minimum hamming distance associated with each of the encoding specifics in the set of encoding specifics;
25. The method of claim 24, wherein choosing the selected encoding specifics is done at least in part based on a detection scheme employed by the base station.
26. The method of claim 25, wherein the modulated uplink control signal is transmitted without non-null pilot signals.
27. The method of claim 24 wherein the chosen encoding specifics is chosen at least in part on the basis of at least one of a desired code length and a size of the uplink control signal.
28. The method of claim 24, further comprising adapting the encoding specifics so as to accommodate at least one of the desired code length and the size of the uplink control signal.
29. The method of claim 28, further comprising using sub-codes to reduce the number of possible encoding outcomes.
30. The method of claim 29, wherein sub-codes are selected through an exhaustive search.
31. The method of claim 28, further comprising reducing the length of the encoded uplink control signal using puncturing on a set of all the possible encoding outcome for the selected encoding specifics.
32. The method of claim 24 wherein each of the encoding specifics in the set of encoding specifics comprises a number of repetitions, and wherein choosing one of the selected encoding specific is done at least in part on the bases of the effect that the number of repetitions will have on the code length.
33. The method of claim 24, wherein each of the encoding specifics in the set of encoding specifics correspond to a block code encoding scheme.
34. The method of claim 33, wherein each of the encoding specifics in the set of encoding specifics correspond to a Reed-Muller encoding scheme.
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US14/270,025 Continuation US9088385B2 (en) 2008-07-07 2014-05-05 Uplink control signal design for wireless system
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US14/803,698 Active US9673932B2 (en) 2008-07-07 2015-07-20 Uplink control signal design for wireless system
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