PATENT DOCUMENT

Publication Number: US-8346205-B2
Application Number: US-201113190384-A
Country: US
Kind Code: B2

Title: Method and system for wireless communications between base and mobile stations

Abstract:
A method and system for wireless communications between base and mobile stations use reference signals transmitted from base stations prior transmission of data signals. The reference signals are used to determine propagation characteristics of communication channels between the base and mobile stations and optimize, in real time, parameters of receivers of the mobile stations for processing the following data signals. Applications of the invention include wireless communication systems compliant with OFDMA, 3GPP LTE, RFN-OFDMA, OFDM, TDMA, and the like communication protocols.

Claims:
1. A method comprising:
 receiving a reference signal having one or more predetermined characteristics; 
 determining at least one propagation characteristic of a communication channel based at least in part on the one or more predetermined characteristics of the received reference signal; 
 adjusting one or more receiver configuration parameters of a receiver based on the determined at least one propagation characteristics of the communication channel; 
 receiving a data signal using the receiver having the adjusted configuration parameters; and 
 wherein the reference signal immediately precedes the data signal. 
 
     
     
       2. The method of  claim 1 , further comprising activating the receiver from a standby state immediately prior to arrival of the reference signal. 
     
     
       3. The method of  claim 2 , wherein the receiver is activated from the standby state according to a predefined schedule. 
     
     
       4. The method of  claim 1 , wherein the data signal is received on the same communication channel. 
     
     
       5. The method of  claim 1 , wherein at least a portion of the data signal is received on a different communication channel. 
     
     
       6. The method of  claim 1 , wherein the reference signal is determined by (i) a time-frequency pattern of reference symbol locations and (ii) amplitude and phase modulation of a sequence applied to the reference symbol locations. 
     
     
       7. The method of  claim 6 , wherein the sequence is further selected from the group consisting of: (i) a Generalized Chirp-Like (GCL) sequence, (ii) a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence, and (iii) a Walsh sequence. 
     
     
       8. A device comprising:
 a wireless receiver having at least one adjustable configuration parameter; and 
 a processor; and 
 a computer readable medium comprising instructions configured to when executed by the processor:
 receive a reference signal having one or more known characteristics; 
 determine an instant propagation characteristic of a communication channel based on the received reference signal only; 
 adjust at least one configuration parameter of the wireless receiver based on the determined propagation characteristic of the communication channel; and 
 receive a data signal using the adjusted wireless receiver. 
 
 
     
     
       9. The device of  claim 8 , further comprising a wireless transmitter. 
     
     
       10. The device of  claim 8 , wherein the computer readable medium further comprises instructions which when executed by the processor activate the device from an inactive mode, based at least in part on a predefined schedule. 
     
     
       11. The device of  claim 8 , wherein the wireless receiver is configured to receive Orthogonal Frequency Division Multiplexed (OFDM) signals. 
     
     
       12. The device of  claim 8 , wherein the wireless receiver is configured to receive the reference signal via at least one subcarrier. 
     
     
       13. The device of  claim 12 , wherein the wireless receiver is configured to receive the data signal via the at least one subcarrier. 
     
     
       14. The device of  claim 12 , wherein the wireless receiver is configured to receive the data signal via at least one different subcarrier. 
     
     
       15. A base station, the base station comprising:
 an antenna; 
 a transmitter coupled to the antenna and adapted for transmitting signals at a first plurality of sub-carrier frequencies; 
 a processor; and 
 a computer readable medium comprising instructions configured to, when executed by the processor, transmit a reference signal and a data signal to at least one mobile station of the system;
 wherein: 
 the mobile station can determine an instant propagation characteristic of a communication channel based on the reference signal only; and 
 the mobile station can adjust its receiver based on the determined instant propagation characteristics of the communication channel to receive the data signal. 
 
 
     
     
       16. The base station of  claim 15 , further adapted to generate the reference signal and the data signal at the same sub-carrier frequency. 
     
     
       17. The base station of  claim 15 , further adapted to generate at least portions of the reference signal or the data signal at different or multiple sub-carrier frequencies. 
     
     
       18. The base station of  claim 15 , wherein the reference signal comprises: (i) a time-frequency pattern of reference symbol locations and (ii) amplitude and phase modulation of a sequence applied to the reference symbol locations. 
     
     
       19. The base station of  claim 15 , wherein the reference signal is selected from the group consisting of a Generalized Chirp-Like (GCL) sequence, a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence, and a Walsh sequence. 
     
     
       20. The base station of  claim 15 , wherein the at least one mobile station comprises a plurality of mobile stations. 
     
     
       21. The base station of  claim 20 , wherein each of the plurality of mobile stations has a corresponding reference signal.

Description:
PRIORITY 
     This application is a continuation of and claims priority to co-owned co-pending U.S. patent application Ser. No. 11/688,125 of the same title filed Mar. 19, 2007, the foregoing incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     The present inventions relates generally to the field of wireless communications, and more specifically, to a method and system for wireless communications between base and mobile stations. 
     2. Related Art 
     In wireless communication system using communication protocols based on time division multiplexing techniques (for example, an Orthogonal Frequency Division Multiple Access (OFDMA) communication protocol), a base station transmits information to a mobile station with pre-determined periodicity during pre-assigned time intervals. To reduce power consumption and extend battery life, between such time intervals a receiver of the mobile station is switched to an energy-saving standby state. 
     However, during periods of time between consecutive transmissions, propagation characteristics of a communication channel between the base and mobile stations may change significantly. As a result, when re-activated, the receiver of the mobile station may not be optimally configured for receiving transmissions from the base station. 
     Despite the considerable effort in the art devoted to development of methods and systems for communications between base and mobile stations, further improvements would be desirable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements, except that suffixes may be added, when appropriate, to differentiate such elements. It is contemplated that features or steps of one embodiment may beneficially be incorporated in other embodiments without further recitation. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. 
         FIG. 1  is a schematic diagram illustrating a portion of a system for wireless communications adapted for implementing an embodiment of the present invention. 
         FIG. 2  is a schematic timing diagram of reference and data signals used in the system of  FIG. 1 . 
         FIG. 3  is a schematic diagram illustrating an exemplary allocation of frequencies of the reference and data signals of  FIG. 2  in the frequency domain. 
         FIG. 4  is a schematic diagram of an exemplary base station of the system of  FIG. 1  in accordance with one embodiment of the present invention. 
         FIG. 5  is a schematic diagram of an exemplary mobile station of the system of  FIG. 1  in accordance with one embodiment of the present invention. 
         FIG. 6  is a flow diagram illustrating a method for transmitting information in the system of  FIG. 1  in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the figures,  FIG. 1  depicts a schematic diagram illustrating a portion of a wireless communication system  100  adapted for implementing an embodiment of the present invention, and  FIG. 2  depicts a schematic timing diagram  200  of reference and data signals used in the system  100  as a function of time (axis  201 ). 
     Generally, the system  100  is compliant with a communication protocol such as an Orthogonal Frequency Division Multiple Access (OFDMA) communication protocol, a Third Generation Partnership Project Long Term Evolution (3GPP LTE) communication protocol, a Random Frequency-Hopping OFDMA (RFN-OFDMA) communication protocol, an Orthogonal Frequency-Division Multiplexing (OFDM) communication protocol, or a time division multiple access (TDMA) communication protocol, among other communication protocols. 
     Illustratively, the system  100  comprises a plurality of base stations  110  and a plurality of mobile stations (or units of user equipment (UE))  120 . The base stations  110  are communicatively selectively coupled to one another via interfaces  130  (for example, wireless (as shown), wired, or optical interfaces), and the mobile stations  120  are selectively coupled to the respective regional base stations  110  via wireless interfaces  140 . 
     In the depicted embodiment, mobile stations  120   1 - 120   N  and  120   N+1 - 120   M  are coupled to the base stations  110   1  and  110   K , respectively, where N, M, and K are integers and M&gt;N. In exemplary applications, a mobile station is wireless communication device such as a cellular phone, a personal digital assistant (FDA), a mobile computer, and the like. 
     Referring to  FIG. 2 , in operation, a base station  110  cyclically transmits to a particular mobile station  120 , with a pre-determined periodicity  230 , a reference signal  210  (denoted as “R”) and a data signal  220  (denoted as “DATA”) carrying information directed to that mobile station. In one embodiment, the data signal  220  constitutes a sub-frame of a downlink in the context of the 3GPP LTE communication protocol. 
     In one embodiment, the reference signal is determined by (i) a time-frequency pattern of reference symbol locations and (ii) amplitude and phase modulation of a sequence applied to the reference symbol locations. For example, the reference symbol locations may be separated, in, the time domain, approximately by integer multiples of 1/14 milliseconds and, in the frequency domain, by multiples of 15 kHz. Typical sequences used to create the amplitude and phase modulation applied to the reference symbol locations have near-zero cross-correlation and near-zero autocorrelation properties. Examples of such sequences include the Generalized Chirp-Like (GCL) sequence, the Constant Amplitude Zero Auto-Correlation (CAZAC) sequence, and the Walsh sequence. 
     In the time domain, the reference signal  210  precedes the respective data signal  220  (for example, a reference signal  210   L  precedes a data signal  220   L , where L is an integer). More specifically, the reference signal  210  and the data signal  220  are transmitted during time intervals  202  and  212 , respectively, which are separated by a time interval  204 . In operation, after receiving the data signal  220  (illustratively, at a moment T 2 ), a receiver of the mobile station  120  is switched from an active state to a standby state until a moment T 1 . The moment T 1  precedes an arrival of the reference signal  210  of the consecutive cycle  230  and, at the moment T 1 , the receiver of the mobile station is switched back to the active state. 
     In one embodiment, the duration of the reference signal  210  is from about 20 to 200 μsec, the duration of the time interval  204  is from about 0.3 to 3 msec, the duration of the data signal  220  is from about 0.5 to 5 msec, and the duration of the time interval  230  is from about 0.5 to 5 see. 
     In operation, during a time interval  214  separating consecutive transmissions of the data signals  220 , propagation characteristics of a communication channel between the base and mobile stations may change substantially enough to have detrimental effect of qualitative parameters of the system  100 . The reference signal  210  is generally a test signal having pre-determined characteristics that is transmitted to the mobile station(s) for determining instant propagation characteristics of the communication channel. Using results of analysis of reception of the reference signal  210 , the mobile station adjusts, in real time, configuration parameters of its receiver to optimize reception of the data signal  220  shortly following the reference signal  210  upon expiration of the time interval  204 . 
       FIG. 3  depicts a schematic diagram  300  illustrating an exemplary allocation of frequencies of the reference and data signals of  FIG. 2  in the frequency domain (x-axis  301 ). In the depicted embodiment, the reference signal  210  is illustratively transmitted at a sub-carrier frequency  302 , and the data signals  220  directed to respective mobile stations  120  are selectively transmitted at sub-carrier frequencies  304 . The frequencies  302  and  304  generally are sub-carrier frequencies of the system  100  and disposed within bandwidths  310  of receivers of the mobile stations  120 . 
     In the depicted embodiment, the reference signal  210  is transmitted at a sub-carrier frequency disposed at a boundary of a bandwidth  310  and allocated at a spectral distance  306  from a particular sub-carrier frequency  304 . In alternate embodiments, any sub-carrier frequency  304  may by used for transmitting the reference signal  210 , as well as the same sub-carrier frequency may used for transmitting both the reference and data signals. Typically, carrier frequencies of the reference and data signals  210 ,  220  are in a range from 400 MHz to 2.6 GHz, sub-carrier frequencies  302 ,  304  are on a 15 kHz raster over 1.25 MHz to 20 MHz bandwidths offset by a respective carrier frequency, and the spectral distance  306  is an integer multiple of 15 kHz. 
     In further embodiments, in consecutive cycles  230 , the reference and data signals  210  and  220  may be transmitted at different sub-carrier frequencies (for example, frequencies changed in pre-selected pattern). Additionally or alternatively, in the time domain, at least portions of the reference and data signals may also be transmitted using different or multiple sub-carrier frequencies. As such, in various embodiments, in the time/frequency continuum, the base station  110  may generate a plurality of the reference signals  210  having the same or different frequencies, where each reference signal precedes the respective data signal  220 , which is directed to a particular mobile station  120  and transmitted at a single or multiple sub-carrier frequencies. 
       FIG. 4  depicts a schematic diagram of an exemplary base station  110  of the system  100  of  FIG. 1  in accordance with one embodiment of the present invention. The base station  110  generally comprises an antenna  402 , a transmitter  410 , a generator  412  of the reference signal  210 , a receiver  420 , a data processor  430 , a program memory  440 , timing circuits  450 , support systems  460 , and interfaces (illustratively, shown as a common bus  404 ) supporting data/command exchanges between components of the base station. 
     Programs of a respective communication protocol implemented in the system  100  are stored in the program memory  440  and, when executed by the data processor  430 , facilitate operability of the base station  110 . In particular, the transmitter  410  and receiver  420  support bi-directional wireless communications between the base station  110  and adjacent base station(s) of the system  100  and between the base station  110  and a plurality of the mobile stations  120 . In operation, the timing circuits  450  generate synchronization signals, which facilitate allocation of pre-determined time slots for uplink and downlink transmissions to each of the mobile stations  120 . Input/output devices, power sources, and the like auxiliary components of the base station  110  are collectively denoted herein as support systems  460 . 
     In the depicted embodiment, the generator  412  is shown as a stand-alone device coupled to the transmitter  410 , however, in an alternate embodiment, the generator  412  may be a portion of the transmitter  410 . Alternatively or additionally, at least portions of the generator  412  may be implemented in software as a computer program stored in the program memory  440  and, in operation, executed by the data processor  430 . In yet another embodiment, the generator  412  may directly be coupled to the antenna  402 . 
       FIG. 5  is a schematic diagram of an exemplary mobile station  120  of the system  100  of  FIG. 1  in accordance with one embodiment of the present invention. The mobile station  120  generally comprises an antenna  502 , a transmitter  510 , a receiver  520 , digital signal processing (DSP) circuits  530 , a memory module  540 , a processor  550 , user interface  560 , auxiliary devices collectively denoted herein as support circuits  570 , a battery  580  powering components of the mobile station, and interfaces (illustratively, shown as a common bus  504 ) supporting data/command exchanges between components of the mobile station. 
     In operation, the processor  550  administers operation of the mobile station  120  by executing programs stored in the memory module  540  and following user instructions entered via the user interface  560 . The user interface  560  may include at least some of a speaker, a microphone, a display, a keyboard, wired or optical connectors, pushbuttons, or indicators, among other devices adapted to facilitate human or machine interactions with a computerized communication device such as mobile station  120 . 
     The DSP circuits  530  generally provide synchronization between the transmitter  510  and receiver  520  and the base station  110 , as well as facilitate support for the user interface  560 . Illustratively, the DSP circuits  530  includes a timer  532  providing, in particular, synchronization between timing of transitions to active/standby states of the transmitter  510  and the reference and data signals  210  and  220  of the base station  110 , as discussed above in reference to  FIG. 2 . In alternate embodiments, at least a portion of functions of the DSP circuits  530  may be implemented in software as a computer program stored in the memory module  540  and, in operation, executed by the processor  550 . 
     Via the antenna  502 , the transmitter  510  and receiver  520  support bi-directional communications between the mobile station  120  and the respective base station  110 . In one embodiment, the receiver  520  includes a demodulator/amplifier  512 , an analog-to-digital converter (ADC)  514 , and a control module  516 . In operation, the receiver  520  receives and processes downlink transmissions from the base station  110 , each such transmission comprising the reference and data signals  210  and  220 , as discussed above in reference to  FIGS. 2-3 . 
     After receiving the reference signal  210 , the control module  516  analyses a corresponding feedback signal forwarded to the module  516  via interface  518 . Based on results of the analysis, the control module  516  determines propagation characteristics of a communication channel between the base and mobile stations and adjusts, in real time, configuration parameters of the demodulator/amplifier  512  to provide optimal conditions for receiving the data signal  220 . In one embodiment, the control module  516  adjusts at least one of a gain, a bandwidth, or an in-phase/quadrature compensation of the demodulator/amplifier  512 , among other configuration parameters of the receiver  520 . 
     In the depicted embodiment, the control module  516  is a stand-alone hardware portion of the receiver  520 , whereas the feedback signal is provided to the module  516 , in a digital format, from the ADC  514 . In an alternate embodiment, the demodulator/amplifier  512  may be a source of the feedback signal provided in an analog format. In further embodiments, some or all portions of the control module  516  may be implemented in software as a computer program stored in the memory module  540  and, in operation, executed by the processor  550 . 
       FIG. 6  depicts a flow diagram illustrating a method  600  for transmitting information in the system  100  of  FIG. 1  in accordance with one embodiment of the present invention. In exemplary applications, the method  600  is used to enhance performance and, in particular, Quality of Service (QoS) characteristics of the system  100 , as well as reduce power consumption in the mobile stations  120 . 
     For brevity, the method  600  is discussed herein in the context of a single base station  110  and a single mobile station  120 . Those skilled in the art will readily appreciate that the same method steps are performed, during cyclically repeated time intervals each defined by the respective adjacent moments T 1  (discussed in reference to  FIG. 2 ), for each mobile station  120  in communication with a particular base station  110 . 
     The method  600  starts at step  610 , where, at the moment T 1  preceding an arrival of the reference signal  210 , the receiver  520  of the mobile station  120  is switched from a standby state to an active state. In one embodiment, the receiver  520  is initially assigned the configuration parameters used in a preceding active state, i.e., prior to switching the receiver to the standby state. Switching the receiver  520  to the active state may be triggered, for example, by a signal generated using the timer  532  synchronized with the timing circuits  450  of the base station  120 . 
     At step  620 , the base station  110  transmits and the mobile station  120  receives the reference signal  210 . An amplitude of the transmitted reference signal  220  is pre-selected to provide, within operating range of the base station  110 , a high signal-to-noise ratio (SNR) of an output signal of the demodulator/amplifier  512  of the receiver  520  and, correspondingly, a high SNR of an output signal of the ADC  514 . The reference signal  210  is transmitted at one of sub-carrier frequencies used in the system  100  and, in different transmissions, may be transmitted at different sub-carrier frequencies. 
     Using a feedback signal produced by the demodulator/amplifier  512  or the ADC  514 , the received reference signal  210  is analyzed using the control module  516  of the receiver  520 . An algorithm used by the control module  516  to analyze the reference signal  210  may be implemented in a form of hardware, software, or a combination thereof in the module  516  or at least portions of the algorithm may be implemented in a form of a computer program stored in the memory module  540  of the receiver  520 . In one embodiment, the algorithm is directed to determining parameters of the Rayleigh fading of the reference signal  210  in the communication channel between the base and mobile stations. 
     At step  630 , using results of the analysis of the reference signal  210 , the configuration characteristics (e.g., gain, bandwidth, in-phase/quadrature compensation, among other parameters) of the receiver  520  are adjusted to provide optimal conditions (e.g., maximum SNR) during reception of the data signal  220 . The receiver  520  having the adjusted configuration characteristics may use the ADC  514  having reduced dynamic range and, consequently, low power consumption. In one embodiment, the analysis of the reference signal  210  is completed and the configuration characteristics are adjusted prior to expiration of the time interval  204 . 
     In one embodiment, when propagation characteristics of the communication channel between the base and mobile stations momentarily deteriorate to a point that the reference signal is missed in the channel, the control module  516  restores/maintains the configuration parameters defined during at least one of most recent transmissions. 
     At step  640 , the base station  110  transmits and the mobile station  120  receives the data signal (i.e., sub-frame)  220 . The data signal  220  is transmitted at one of the sub-carrier frequencies  404  that may either be equal to or different from the sub-carrier frequency of the reference signal  210 , as well as may hop during the transmission (i.e., during time interval  212 ) or differ from one transmission to another. Using the receiver  520  having its configuration characteristics adjusted as discussed above in reference to steps  620  and  630 , the mobile station  120  provides, at minimal power consumption, reception of the data signal  220  with a peak SNR. 
     At step  640 , after receiving the data signal  220 , at the moment T 2 , the receiver  520  is switched from the active state to the energy-saving standby state. A transition to the standby state may be initiated using, for example, a signal produced by the timer  532 . To preserve resources of the battery  580 , the receiver  520  is maintained in the standby state until the moment T 1  of the next transmission cycle  230 , where the steps of method  600  are repeated, as shown with a link  602 . 
     In a further embodiment, the system  100  may be a Multiple-Input Multiple-Output (MIMO) wireless communication system using multiple antennas at the base and mobile stations and employing at least one of beamforming, spatial multiplexing, or diversity coding techniques. 
     In one example of a MIMO system, the antenna  402  of the base station  110  would represent a composite antenna having multiple, specially separated antenna structures. Each antenna structure is selectively adapted for transmitting same or different signals at pre-selected pluralities of sub-carrier frequencies. Correspondingly, in said MIMO embodiment, the antenna  502  of the mobile station  120  may also be a composite antenna having multiple antenna units each selectively adapted for receiving particular portions of signals transmitted by the base station  110 . In this embodiment, the receiver  520  would be a multi-section unit, where each section includes the demodulator/amplifier  512 , ADC  514 , and a control module  516 . Inputs and outputs of these sections are selectively coupled to particular antennas units of the composite antenna  502  and to the common bus  504 , respectively. 
     In operation, in such a MIMO system a plurality of communication channels is established, at multiple sub-carrier frequencies, between the antenna structures of the base and the antenna units of the mobile stations, and the reference and data signals  210  and  220  are transmitted through these channels or pre-determined portions thereof. Using the reference signal  210 , configuration parameters of each section of the multi-section receiver  520  are adjusted, prior to arrival of the data signal  220 , as discussed above in reference to  FIG. 6 . 
     As used herein, a software system can include one or more objects, agents, threads, subroutines, separate software applications, two or more lines of code or other suitable software structures operating in one or more separate software applications, on one or more different processors, or other suitable software architectures. 
     As will be appreciated, the processes in preferred embodiments of the present invention may be implemented using any combination of computer programming software, firmware or hardware. As a preparatory step to practicing the invention in software, the computer programming code (whether software or firmware) according to a preferred embodiment will typically be stored in one or more machine readable storage mediums such as fixed (hard) drives, diskettes, optical disks, magnetic tape, semiconductor memories such as read-only memories (ROMs), programmable ROMs (PROMs), etc., thereby making an article of manufacture in accordance with the invention. The article of manufacture containing the computer programming code is used by either executing the code directly from the storage device, by copying the code from the storage device into another storage device such as a hard disk, random access memory (RAM), etc., or by transmitting the code for remote execution. The method form of the invention may be practiced by combining one or more machine-readable storage devices containing the code according to the present invention with appropriate standard computer hardware to execute the code contained therein. An apparatus for practicing the invention could be one or more computers and storage systems containing or having network access to computer program(s) coded in accordance with the invention. 
     Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. Also the invention is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. Any benefits, advantages, or solutions to problems that are described herein with regard to specific embodiments are not intended to be construed as a critical, required, or essential feature or element of any or all the claims.

Metadata:
Filing Date: 20110725
Publication Date: 20130101
Grant Date: 20130101
Priority Date: 20070319
Inventors: DEHNER LEO G.
MCCOY JAMES W.
TRAYLOR KEVIN B.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W52/0225", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B17/382", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/382", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/16", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0225", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 39774597