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Cooperative differential space-time spreading for the asynchronous relay aided CDMA uplink using interference rejection spreading code

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  • Design
  • Mathematics


untitled IEEE SIGNAL PROCESSING LETTERS, VOL. 17, NO. 2, FEBRUARY 2010 113 Cooperative Differential Space–Time Spreading for the Asynchronous Relay Aided CDMA Uplink Using Interference Rejection Spreading Code Shinya Sugiura, Member, IEEE, Sheng Chen, Fellow, IEEE, and Lajos Hanzo, Fellow, IEEE Abstract—This letter proposes a differential Space–Time Coding (STC) scheme designed for asynchronous cooperative networks, where neither channel estimation nor symbol-level synchroniza- tion is required at the cooperating nodes. More specifically, our system employs differential encoding during the broadcast phase and a Space–Time Spreading (STS)-based amplify-and-forward scheme during the cooperative phase in conjunction with inter- ference rejection direct sequence spreading codes, namely Loosely Synchronized (LS) codes. Our simulation results demonstrate that the proposed Cooperative Differential STS (CDSTS) scheme is ca- pable of combating the effects of asynchronous uplink transmis- sions without any channel state information. Index Terms—Asynchronous cooperation, cooperative diversity, differential space–time spreading, loosely synchronized codes. I. INTRODUCTION C OOPERATIVE Space–Time Coding (STC) schemes [1]were proposed to achieve the best attainable diversity gain of uncorrelated elements, where a collection of single-an- tenna-aided nodes act as a virtual antenna array, having widely separated distributed antenna elements. On the other hand, attaining a high cooperative space–time diversity gain in a practical relay-aided network imposes further challenges. Firstly, many of the previously-proposed cooperative STC schemes assumed that perfect Channel State Information (CSI) of the Source-Relay (SR) links and/or of the Relay-Destination (RD) links is available at the destination receiver. However, the rapidly changing topology of vehicles travelling at high speeds makes it challenging to acquire accurate CSI, which results in a severe degradation of the achievable performance. By contrast

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