Throughput is an important performance measure for data communications over wireless links. In this work, we consider joint adaptation of coding rates, modulation modes and level of cooperation for cooperative relaying to maximize the data throughput. We consider five different schemes with joint adaptation based on channel statistics: Direct transmission, conventional multihop, stationary and dynamic coded cooperation, cooperative multihop. We first obtain closed form expressions for the throughputs achieved by these schemes. Considering channel coding and modulation schemes used in wireless local area standard (WLAN) IEEE 802.11, we then compute the best throughputs and provide performance comparisons. Our results show that coded cooperation with adaptation provides substantial improvement over direct transmission and conventional multi- hop. Cooperative multihop enables further improvements over coded cooperation by fully exploiting cooperative diversity as well as rate adaptation and achieves the highest throughput performance among these five transmission schemes. We also observe that to maximize the data throughput in direct transmission and conventional multihop, adaptation for each hop only depends on the channel quality from the transmitter to the receiver. However, in cooperative strategies a system wide optimization is necessary.

User cooperation is an efficient approach to obtain diversity in both centralized and distributed wireless networks. In this paper, we consider a coded cooperative system under quasi-static Rayleigh fading and investigate the partner-choice problem. We find conditions on the interuser and user-to-destination channel qualities for cooperation to be beneficial. Using frame-error rate (FER) as a metric, we define the user cooperation gain (G) for evaluating the relative performance improvement of cooperative over direct transmissions when a particular channel code is used. We introduce the cooperation decision parameter (CDP), which is a function of user-to-destination average received signal-to-noise ratios (SNRs), and demonstrate that whether cooperation is useful or not ($G≫1$or$G≪1$) depends only on the CDP, not the interuser link quality. We use an analytical formulation of the CDP to investigate user cooperation gain and provide insights on how a user can choose among possible partners to maximize cooperation gain. We first consider the asymptotic performance when one or both partners have high average received SNR at the destination. We then provide conditions on user and destination locations for cooperation to be beneficial for arbitrary SNRs. We illustrate these cooperative regions and study geometric conditions for the best partner choice. We also define the system cooperation gain and illustrate cooperation benefit for both users. All of our theoretical results are verified through numerical examples.

User cooperation is an efficient approach to obtain diversity in both centralized and distributed wireless networks. In this paper, we consider a coded cooperative system under quasi-static Rayleigh fading and investigate the partner-choice problem. We find conditions on the interuser and user-to-destination channel qualities for cooperation to be beneficial. Using frame-error rate as a metric, we define the user cooperation gain (G) for evaluating the relative performance improvement of cooperative over direct transmission when a particular channel code is used. We introduce the cooperation decision parameter (CDP), which is a function of user-to-destination average received signal-to-noise ratios (SNRs), and demonstrate that whether cooperation is useful or not (G>1 or G<1) depends only on the CDP, not the interuser link quality. We use an analytical formulation of the CDP to investigate user cooperation gain and provide insights on how a user can choose among possible partners to maximize cooperation gain. We first consider the asymptotic performance when one or both partners have high average received SNR at the destination. We then provide conditions on user and destination locations for cooperation to be beneficial for arbitrary SNRs. We illustrate these cooperative regions, and study geometric conditions for the best partner choice. We also define the system cooperation gain and illustrate cooperation benefits for both users. All of our theoretical results are verified through numerical examples

Cooperation provides an efficient form of diversity in wireless communications. In this paper we consider a coded cooperative system where the source and the relays may have multiple antennas. We describe two simple algorithms for choosing a good relay: blind-selection-algorithm and informed-selection-algorithm. These algorithms only require the knowledge of average received signal to noise ratios at the destination. Simulation results, carried out for a cellular system, show that both algorithms result in substantial improvement over direct transmission and random choice of relay in the cell and provide error rates close to best relay performance.

Cooperation of mobiles provides signal diversity in wireless networks. We consider a coded cooperative system under Rayleigh fading and path loss. For an arbitrary signal to noise ratio, we find conditions on the user geometry for two-user cooperation to be beneficial. We find that whether cooperation is useful or not is only determined by the cooperation decision parameter (CDP). We illustrate regions for which cooperation results in a gain in frame error rate (FER) for individual users and use the analytical formulation of the CDP to investigate how locations of the user and the partner affect the user cooperation gain. Our analytical results also provide insights on how a user can choose among many partners to maximize cooperation gain. All of our theoretical results are verified by numerical simulations of the FER.

The use of orthogonal spreading codes has attracted much attention due to their ability to suppress interference from other users, compared with the nonorthogonal sequences in the synchronous case. In this paper, new sets of orthogonal sequences derived from the unified complex Hadamard transforms (UCHTs) are investigated. Various correlation properties of the sequences are mathematically derived and analyzed. It is shown that some UCHT sequences provide better autocorrelation properties than orthogonal Walsh-Hadamard sequences. Performance comparisons between UCHT sequences, Gold, small set of Kasami, and m-sequences show that some UCHT sequences outperform these well-known spreading sequences under simulation of systems in the presence of multiple access interference and additive white Gaussian noise.