Distributed Space-Frequency Block Coding In Cooperative Wireless Communications

Wireless channel fading is one of the key factors that impact twireless communication performance. The diversity is an attractive way to combat fading by transmitting a number of signals and its copies experienced independent fading. Multiple Input Multiple Output (MIMO) antenna is a typical spatial diversity technique, by combining multiple antennas space-time block coding with orthogonal frequency division multiplexing (OFDM) forming space-frequency block coding, In multipath channel fading conditions, which also can get additional frequency diversity gain. This paper discusses several space-frequency block coding schemes, and compares them via simulation.As the power consumption, size and cost constraints, It is difficult for a mobile terminal to equip with multiple antennas. Cooperative diversity is a kind of spatial diversity technique that multiple users equipping with cooperating with single antenna work together, and share their antenna resources to form a virtual multi antennas system. The distributed space-frequency block coding applies the space-frequency block coding to cooperative communication, coding by cooperative relay nodes collaborate with each other. This paper investigates the coding cooperation process and diversity performance of the distributed space-frequency block coded under two cases, which considering whether a direct forward link exists, between the source and the destination.For lacking of forward direct transmission Link between the source and the destination, this paper investigates the diversity performance of an amplify-and-forward (AF) coding scheme and a decode-and-forward(DF) coding scheme, based on the symmetry channels structure among all nodes, and gives an AF/DF hybrid coding scheme. It is shown that all the three kinds of coding schemes have the same diversity gain which includes a cooperative diversity gain and a frequency diversity gain, and the AF/DF hybrid coding scheme has better coding gain. To the DF coding scheme, this paper analyze and simulate the diversity performance under asymmetric link among all nodes, The results showed that this coding scheme can ensure full cooperative diversity, and the frequency diversity gain is affected by the link channel multipath numbers between nodes.To considering the forward direct transmission link between source and destination, this paper analyze and simulate the coding diversity performance of all the three coding schemes. For different user cooperative transmission protocols(UCTP), the result shows that, for different UCTP, the three distributed space-frequency coding schemes have the same diversity gain, and the AF/DF hybrid coding scheme has better coding gain. For any coding scheme, the diversity performance is distinctive under different UCTP, it is mainly due to the different Utilization of frequencies resources. This paper also presents two kinds of cooperative model that node helps to relay data each other, based on the orthogonal frequency division multiple access(OFDMA), with the advantage of flexible subcarrier allocation and higher resource utilization.