Achievable Rates for Two User Cooperative OFDMA

Abstract

Abstract-We propose two encoding strategies for a two user cooperative Orthogonal Frequency Division Multiple Access (OFDMA) system, based on block Markov superposition encoding. We obtain the expressions for the resulting achievable rate regions for both encoding strategies, and evaluate them through simulations. We show that, by allowing for re-partitioning and re-encoding of the cooperative messages across subchannels, it is possible to better exploit the diversity created by OFDMA, and higher rates can be achieved.

Optimum power control for transmitter cooperation in OFDMA based wireless networks

“…The achievable rate region for the ISCE strategy is obtained by running this algorithm for varying priorities µ k , and then by taking a convex hull over the resulting power optimized regions. In Figure 3, we compare the achievable rate region for power controlled cooperative OFDMA with those for several enconding strategies without power control, from [1]. We assume that, for the channel non-adaptive protocols, the TXs are still able to allocate their total power across subchannels and codewords.…”

“…To establish the cooperation among the TXs, we employ a channel adaptive version of the ISCE proposed in [1]. In ISCE, the message of each TX k ∈ {1, 2} is divided into two submessages, w k0 and w kj , intended to be decoded at the RX and cooperative partner j ∈ {1, 2} respectively, which are further divided into N submessages each,…”

“…The decoding at the RX is performed using backwards decoding [5]. Note that, [1] does not utilize instantaneous CSI to adapt the instantaneous transmission powers. In order to further take advantage of the diversity provided by the OFDMA system, in this paper, we propose a channel adaptive version of the encoding strategy in [1], where we scale each of the above codewords by variable powers,…”

“…In this paper, we obtain the optimum PA policies that maximize the rate region achievable by the full-duplex ISCE strategy of [1]. Despite the complex re-encoding structure employed in ISCE, and the fact that the powers allocated to each subchannel have to satisfy a sum power constraint over subchannels, the achievable rate region turns out to be of a relatively similar form to its scalar counterpart, and we are able to extend some properties of the optimal PA derived in [7] for scalar cooperative MAC, to cooperative OFDMA.…”

“…However, these works consider either a one sided cooperation strategy, or a mutually cooperative strategy based on two parallel dedicated relay channels, or mutual cooperation based on a time division protocol. A more general cooperative OFDMA model based on parallel MAC-GFs, which does not make any prior assumptions about the way in which the subchannels are assigned to the TXs, was introduced in [1], but there, PA as a function of fading states, which can further take advantage of the temporal diversity over each subchannel, was not considered.…”