Capacity Gain from Two-Transmitter and Two-Receiver Cooperation

Capacity improvement from transmitter and receiver cooperation is investigated in a two-transmitter, two-receiver network with phase fading and full channel state information available at all terminals. The transmitters cooperate by first exchanging messages over an orthogonal transmitter cooperation channel, then encoding jointly with dirty paper coding. The receivers cooperate by using Wyner-Ziv compress-and-forward over an analogous orthogonal receiver cooperation channel. To account for the cost of cooperation, the allocation of network power and bandwidth among the data and cooperation channels is studied. It is shown that transmitter cooperation outperforms receiver cooperation and improves capacity over non-cooperative transmission under most operating conditions when the cooperation channel is strong. However, a weak cooperation channel limits the transmitter cooperation rate; in this case receiver cooperation is more advantageous. Transmitter-and-receiver cooperation offers sizable additional capacity gain over transmitter-only cooperation at low SNR, whereas at high SNR transmitter cooperation alone captures most of the cooperative capacity improvement.Comment: Accepted for publication in IEEE Transactions on Information Theor

The Impact of CSI and Power Allocation on Relay Channel Capacity and Cooperation Strategies

Capacity gains from transmitter and receiver cooperation are compared in a relay network where the cooperating nodes are close together. Under quasi-static phase fading, when all nodes have equal average transmit power along with full channel state information (CSI), it is shown that transmitter cooperation outperforms receiver cooperation, whereas the opposite is true when power is optimally allocated among the cooperating nodes but only CSI at the receiver (CSIR) is available. When the nodes have equal power with CSIR only, cooperative schemes are shown to offer no capacity improvement over non-cooperation under the same network power constraint. When the system is under optimal power allocation with full CSI, the decode-and-forward transmitter cooperation rate is close to its cut-set capacity upper bound, and outperforms compress-and-forward receiver cooperation. Under fast Rayleigh fading in the high SNR regime, similar conclusions follow. Cooperative systems provide resilience to fading in channel magnitudes; however, capacity becomes more sensitive to power allocation, and the cooperating nodes need to be closer together for the decode-and-forward scheme to be capacity-achieving. Moreover, to realize capacity improvement, full CSI is necessary in transmitter cooperation, while in receiver cooperation optimal power allocation is essential.Comment: Accepted for publication in IEEE Transactions on Wireless Communication

Improved Achievable Rates for User Cooperation and Relay Channels

Conference PaperIn this paper, we derive a new achievable rate region for the user cooperation channel, which exceeds the best known result for this channel [Wil83]. Since the user cooperation channel includes many other known channels as a special case, the new rate region provides an improved achievable rates for many of the special cases (discussed later). The most notable example is that of the Gaussian relay channel [CG79], for which we present a new closed form inner bound higher than the only known result (Theorem 5 in [CG79]). The basic idea of the proposed encoding and decoding scheme is easier to grasp for a simpler case, the relay channel, by keeping in mind the following Markovian scheme from [CG79]. In Markovian encoding, the relay decodes everything in the current block and uses it to establish a basis for common information sent from the transmitter and relay in the next block. The fact that Markovian coding does not achieve capacity depends on to two inter-related facts: (a) the relay decodes each codeword completely, and (b) discards the residual after decoding; this limits the relay channel capacity to the capacity between the source and the relay. Our proposed encoding does not require the relay to necessarily decode the whole codeword from the transmitter. In addition, the relay \source" encodes the whole received signal some implicit embedding of with the decoded information. Note that the signal transmitted by the relay is not separable into a source code and a channel code. For the user cooperation channel, the above operation is performed by both users for each others' signal

İşbirlikçi bilişsel radyo sistemleri için kodlama ve kod çözme teknikleri, erişilebilir veri hızları ve kaynak tahsisi

İşbirlikli iletişim ve bilişsel radyo, yeni nesil kablosuz haberleşme ağlarında kapasite ve iletişim kalitesinin artırımı için kilit tekniklerdir. Bu tekniklerin her ikisi de, çevrelerinin farkında olan ve bu farkındalığı gönderim stratejilerini belirlerken kullanabilen akıllı düğümlere dayalı olduğundan, yeni nesil protokollerin tasarımında bir arada ele alınmaları son derece doğaldır. Bu projenin temel amacı, kablosuz ağlarda bu iki tekniği bir arada kullanabilen yeni işbirliği stratejileri geliştirmek, ve bunlar ile elde edilebilecek veri hızlarını özkaynakların verimli tahsisi ile eniyilemektir. Projede, iki kullanıcı - tek alıcılı, üç kullanıcı - tek alıcılı, çok kullanıcı - tek alıcılı ve çok kullanıcı - çok alıcılı olmak üzere dört farklı işbirlikli çoklu erişim modeli ele alınmıştır. Bunların ilk üçünde, birincil kullanıcılara belirli veri hızı garantileri sağlanırken, ikincil kullanıcıların ya da tüm sistemin veri hızlarını eniyileyen güç tahsisi algoritmaları geliştirilmiştir. Çok kullanıcı - tek alıcılı sistemde, birincil ve ikincil kullanıcılar arası işbirliği çiftler halinde modellendiğinden, ayrıca en iyi işbirlikçi ortak seçimi de ele alınmıştır. Çok kullanıcı – çok alıcılı hücresel sistem modelinde ise, kullanıcıların hem işbirlikçi ortak, hem de alıcı seçimini güç tahsisi ile birlikte veri hızlarını en büyükleyecek şekilde seçebilecekleri bir kaynak tahsisi algoritması geliştirilmiş, hücre kenarındaki kullanıcılar arasında işbirliğini ve alıcı seçimini mümkün kılmak amacıyla özgün bir zıt kısmi frekans tekrarı modeli önerilmiştir. Ele alınan tüm problemlerde, veri hızlarının aynı miktarda kaynak kullanılmasına karşın yardımlaşma sayesinde kayda değer biçimde artırılabildiği gösterilmiştir. Sonuç olarak, proje kapsamında bilgi kuramsal yaklaşımlarla elde edilen temel sonuçlar bilişsel radyo ile işbirlikli iletişimin kablosuz ağlarda bir arada ele alınmasının faydasına ve gerekliliğine işaret etmektedir.Cooperative communication and cognitive radio are key techniques for increasing the capacity and quality of service of the next generation wireless communication networks. Both of these techniques rely on intelligent nodes, which are aware of their surroundings, and are capable of using this awareness to determine their transmit strategies. Therefore, it is quite natural to consider the joint use of these techniques in the design of next generation communication protocols. The main goal of this project is to develop new cooperation strategies capable of combining cognition and cooperation in wireless networks, and to optimize the rates achievable by these strategies via efficient utilization of the available resources. In this project, we consider four different cooperative multiple access models: two user - single receiver; three user - single receiver, multi user - single receiver and multi user – multi receiver models. The first three models aim to optimize either the rates of the secondary users, or the sum rate of the system, under hard single user rate guarantees for primary users, via power control. In the multi user - single receiver model, the cooperation among the primary and secondary users is modeled as pairwise cooperation, hence, in this scenario, we also solve the optimal partnering problem. In the multi user - multi receiver cellular model, we obtain the jointly optimal power allocation, receiver selection and cooperating partner selection policies that maximize the sum rate of the system. In order to facilitate cooperation among the cell edge users, and receiver selection, we propose a novel complementary fractional frequency reuse scheme, directly tailored for cognitive cooperation. In all of the problems that were considered, it was shown that despite the same amount of total resources being used, the achievable rates can be increased significantly, thanks to cooperation. In conclusion, the fundamental results obtained in this project, based on information theoretic approaches, point to the usefulness, and the necessity of joint consideration of cognition and cooperation in wireless networks.TÜBİTA