Abstract:
Disclosed in some examples is a method performed by a relay station, the method including receiving at a relay station a data packet transmitted from a base station to a subscriber station; receiving a non-acknowledgement (NACK) message transmitted from the subscriber station to the base station in response to the data packet; receiving resource allocation information transmitted from the base station to the subscriber station; and transmitting, in response to the received NACK message at the transmission time, the data packet to the subscriber station in a resource allocation allocated for a retransmission of the data packet from the base station to the subscriber station, wherein the resource allocation is determined from the resource allocation information.

Description:
TECHNICAL FIELD 
     Various embodiments described herein relate to apparatus, and methods associated with wireless communication. Some embodiments relate to Worldwide Interoperability for Microwave Access (WiMAX) networks and 3rd Generation Partnership Project (3GPP) Long-Term-Evolution (LTE) networks. Some embodiments relate to communications, data transmission and relay techniques between base stations (BS) and subscriber stations (SS). 
     BACKGROUND 
     In the wireless environment where subscriber stations may be located near the edge of the coverage area, co-channel interference from a neighboring base station can limit performance. This issue may be exacerbated by shadow fading, where interposing structures or terrain can block the direct transmission path from a serving base station to a subscriber station. Currently, relay stations may be used to improve transmission quality. These relay stations may be other subscriber stations or scaled down base stations. One issue with this approach is the overhead to allocate resources and maintain the relay links. There are also security issues with this approach. 
     Thus, there are general needs for apparatus and efficient methods to relay data between a base station and subscriber station. There are also general needs to relay data with reduced overhead and lower transmission power while maintaining security. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a base station, relay stations and subscriber station of a wireless network in accordance with some embodiments; 
         FIG. 2  illustrates a transmission timeline between the base station, relay stations and subscriber station, in accordance with some embodiments; 
         FIG. 3  illustrates localized and distributed resource allocation, in accordance with some embodiments; 
         FIG. 4  illustrates a procedure for a downlink relay in accordance with some embodiments; 
         FIG. 5  illustrates a procedure for base station support of a relay in accordance with some embodiments; and 
         FIG. 6  illustrates a functional block diagram of a relay station in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims. 
       FIG. 1  illustrates a base station, relay stations and subscriber station of a wireless network in accordance with some embodiments. Wireless network  100  includes a base station (BS)  102 , one or more relay stations (RS 1 )  104 , (RS 2 )  106 , a subscriber (or mobile) station (SS)  108  and a neighbor base station  116 . In some embodiments, the wireless network  100  may be a Worldwide Interoperability for Microwave Access (WiMAX) network, although this is not a requirement. In some embodiments, the wireless network  100  may be a 3rd Generation Partnership Project (3GPP) Long-Term-Evolution (LTE) network, although this is not a requirement. In some embodiments, SS  108  may be configured to receive signals in accordance with the IEEE 802.16x standards for wireless metropolitan area networks (WMANs) including variations and evolutions thereof, although the scope of the invention is not limited in this respect as they may also be suitable to transmit and/or receive communications in accordance with other techniques and standards. For more information with respect to the IEEE 802.16 standards, please refer to “IEEE Standards for Information Technology—Telecommunications and Information Exchange between Systems”—Metropolitan Area Networks—Specific Requirements—Part 16: “Air Interface for Fixed Broadband Wireless Access Systems,” May 2005 and related amendments/versions. For more information with respect to LTE standards, see the 3rd Generation Partnership Project (3GPP) standards for UTRAN-LTE, release 8, March 2008, including variations and evolutions thereof. 
     The direct path signal  114  from BS  102  to SS  108  may be attenuated by blocking structure  110 . Additionally, SS  108  may receive co-channel interference from neighbor base station  116 . RS 1   104 , however, may receive a strong signal  112  from BS  102 . RS 1   104  may also be closely located to SS  108  or otherwise enjoy an acceptable transmission path to SS  108 . In this case RS 1   104  may forward data from BS  102  to SS  108  on a downlink path. Similarly, RS 1   104  may forward data from SS  108  to BS  102  on an uplink path. Any number of alternative relay stations, for example RS 2   106 , may also perform this relay service. This may be preferable to increasing the transmission power of BS  102  since that may increase interference in neighboring cells. The relay stations which may have lower antenna height, lower transmission power and may be located closer to SS  108 , may be less likely to cause interference in neighboring cells. 
     Forwarding messages may be inefficient, however, due to the increased control signalling overhead and resource sharing necessary for this cooperative scheme between the BS  102  and the relay stations  104 ,  106 . Additionally, there may be security concerns with this method. 
       FIG. 2  illustrates a transmission timeline between the base station, relay stations and subscriber station, in accordance with some embodiments. The transmission timeline depicts an efficient method for an implicit relay of data between BS  102  and SS  108  in accordance with some embodiments, where the base station may not need to identify the cooperating relay stations and may operate as if there were no relay stations. 
     The base station  102  sends resource allocation information  205  and a data packet  210  to the subscriber station  108 . Due to co-channel interference and/or a shadow effect the subscriber station may receive a corrupted packet and respond with a non-acknowledgment (NACK)  220 . Relay stations RS 1   104  and RS 2   106 , which may be in idle mode, may overhear the resource allocation information  205 , data packet  210  and NACK packet  220 . After receiving the NACK, the base station may retransmit the data packet. The retransmission may be a hybrid automatic repeat request (H-ARQ) packet  230 . The relay stations may realize that a retransmission is necessary, based on the overheard NACK  220 . One or both of the relay stations  104 ,  106  may generate the same retransmission packet as the base station and may transmit them on the same frequency and time allocation, using the overheard data packet and the overheard allocation information. The retransmission packets from RS 1   104  and/or RS 2   106  may also be H-ARQ packets  240 ,  250 . 
     Thus, the received signal power at the subscriber station may be boosted by the retransmission from RS 1   104  and/or RS 2   106  and the subscriber station may enjoy a better communications link. In this sense, the relay stations may be considered to act as a power booster rather than a conventional relay. The base station may treat the relay stations as part of a multipath channel, like a reflective object with a long delay memory. This may allow for the base station to merely adapt to the multipath channel rather than having to control the relay stations. 
     In some embodiments, the operator of the relay stations  104 ,  106  may get incentives for performing the implicit relay. The operator may need to certify the relay stations so that they automatically perform the relay function when they have surplus power supply. 
       FIG. 3  illustrates localized and distributed resource allocation, in accordance with some embodiments. In accordance with some embodiments, the retransmission may be restricted to a localized resource allocation in frequency and time  310 . In these embodiments, the signals of the base station and the relay stations may cause destructive interference or fading which may result in poor signal quality at the subscriber station. This effect may be exacerbated in the absence of spatial diversity. In accordance with some embodiments, the retransmission may be distributed over multiple frequency and time subbands  320  so that the received power at the subscriber station may be more stable and result in higher signal quality. The improvement may be by a factor of N, where N is the number of multipath reflections. Since the base station and the relay station transmit the same signal to the subscriber station, the data symbols and pilot symbols may be aligned and the subscriber station may perceive the aggregate channel response that needs to be estimated for demodulating data symbols. 
       FIG. 4  illustrates a procedure for a downlink relay in accordance with some embodiments. Procedure  400  may be performed by a relay station, such as relay station  104  ( FIG. 1 ). Operation  410  comprises receiving a data packet transmitted from the base station to a subscriber station. Operation  420  comprises receiving an NACK transmitted from the subscriber station to the base station. Operation  430  comprises receiving resource allocation information transmitted from the base station to the subscriber station. Operation  440  comprises transmitting the data packet to the subscriber station using the resource allocation information. This transmission may be on a distributed resource allocation  450 . Operation  460  comprises receiving a key from the base station which may be used to decode a data packet, the NACK, or the resource allocation information. Operation  470  comprises sending a message to the base station reporting the total amount of data that has been forwarded to or from the subscriber station. 
     Since the relay station may be close to the subscriber station, ranging may not be needed between the two. Furthermore, the relay station may infer the timing for the relay transmission using the existing ranging data for its link to the base station and assuming zero distance to the subscriber station. 
       FIG. 5  illustrates a procedure for base station support of a relay in accordance with some embodiments. Procedure  500  may be performed by a base station, such as base station  102  ( FIG. 1 ). Operation  510  comprises detecting the operation of an implicit relay based on receiving an initial NACK from the subscriber station, performing subsequent transmissions to the subscriber station at reduced power and receiving continuous ACKs from the subscriber station in response to those transmissions. Operation  520  comprises further reducing transmit power to the subscriber station in response to the detection of the implicit relay. Said that base station may cause more interference to the neighboring cell than the relay station due to the higher antenna mounting at the base station, it is desirable to reduce the transmission power of the base station for interference mitigation. 
     In some embodiments, the base station may transmit a signal to interference plus noise ratio (SINR) threshold for data packets to the relay station at operation  530 . In some embodiments, the base station may transmit a signal to interference plus noise ratio (SINR) threshold for NACK to the relay station at operation  540 . The participation of relay stations may be optimized by using these signal quality thresholds. This threshold requirement may effectively shrink the number of cooperating relays to only those that are most effective. Qualified relay stations may thus come from the region whose signal quality is good enough to receive both the data packet from the base station and the NACK from the subscriber station. 
     In some embodiments the base station may perform joint diversity coding with the relay station at operation  550 . For example, the base station may send symbols for the first antenna of an Alamouti code and the relay stations may send symbols for the second antenna of the Alamouti code. Additionally, since the base station or the relay station may not need to use all of the available antennas, the extra antennas may be used for further diversity enhancement schemes or for beamforming. MIMO spatial multiplexing may also be used if the effective channel quality of the retransmission is sufficiently high. In some embodiments, the code symbols for the second antenna are predefined in the system to reduce control overhead. 
     In some embodiments, the base station may transmit a key to the relay station to be used for decoding data packets, NACKs or resource allocation information. For security purposes, scrambling may still be applied to the data since the relay station only needs to decode the scrambled data. 
     In some embodiments, only trusted devices may be allowed to overhear even the scrambled data and NACK. Subscriber stations may have a list of trusted subscribers stored at the base station. The base station may then grant the key only to the trusted subscribers. 
     Although the individual operations of procedure  400  and  500  are illustrated and described as separate operations, one or more of the individual operations may be performed concurrently, and nothing requires that the operations be performed in the order illustrated. Furthermore, some operations may be optional. 
       FIG. 6  illustrates a functional block diagram of a relay station in accordance with some embodiments. Relay station  600  may include transceiver circuitry  604  and processing circuitry  606 . Transceiver circuitry  604  may be coupled to one or more antennas  608  for transmitting and receiving signals from base stations, such as base station  102  ( FIG. 1 ) and subscriber stations, such as subscriber station  108  ( FIG. 1 ). Relay station  600  may be suitable for use as any of relay stations  104  and  106  ( FIG. 1 ). 
     In accordance with some embodiments, the relay station  600  may be configured to operate in a wireless packet-carrying network. In these embodiments, the transceiver circuit  604  may receive a data packet, an NACK and resource allocation information transmitted from a base station to a subscriber station. The transceiver circuit  604  may further transmit the data packet to the subscriber station in response to the NACK. In these embodiments, the processing circuitry  606  may decode the resource allocation information and set the transmission of the data packet to the subscriber station in a retransmission allocation of the data packet from the base station to the subscriber station using the resource allocation information. 
     In some embodiments, the transceiver circuit  604  may transmit the data packet to the subscriber station on a distributed resource allocation. In some embodiments, the transceiver circuit  604  may receive a key from the base station and the processing circuit  606  may use the key to decode the data packet, the NACK or the resource allocation information. 
     In some embodiments, relay station  600  may be part of a portable wireless communication device, such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a smart phone, or other device that may receive and/or transmit information wirelessly. 
     Antennas  608  may comprise one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other types of antennas suitable for transmission of RF signals. In some embodiments, instead of two or more antennas, a single antenna with multiple apertures may be used. In these embodiments, each aperture may be considered a separate antenna. In some multiple-input multiple-output (MIMO) embodiments, antennas  608  may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result between each of antennas  608  and the antennas of a transmitting station. 
     Although relay station  600  is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, application specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements of relay station  600  may refer to one or more processes operating on one or more processing elements. 
     Embodiments may be implemented in one or a combination of hardware, firmware and software. Embodiments may also be implemented as instructions stored on a computer-readable storage medium, which may be read and executed by at least one processor to perform the operations described herein. A computer-readable medium may include any tangible medium for storing in a form readable by a machine (e.g., a computer). For example, a computer-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, and flash-memory devices. 
     The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.