Near-Capacity Turbo Coded Soft-decision Aided DAPSK/Star-QAM for Amplify-and-Forward based Cooperative Communications

Multilevel Differential Amplitude and Phase-Shift Keying (DAPSK) schemes do not require any channel estimation, which results in low complexity. In this treatise we derive the soft-output probability formulas required for a soft-decision based demodulation of high-order DAPSK, in order to facilitate iterative detection by exchanging extrinsic information with an outer Turbo Code (TC). Furthermore, when the TC block size is increased, the system operates closer to the channel capacity. Compared to the identical-throughput TC assisted 64-ary Differential Phase-Shift Keying (64-DPSK) scheme, the 4-ring based TC assisted 64-ary DAPSK arrangement has a power-efficiency improvement of 2.3 dB at a bit error rate (BER) of 10-5 . Furthermore, when the TC block size is increased, the system operates closer to the channel capacity. More specifically, when using a TC block length of 400 modulated symbols, the 64 DAPSK (4, 16) scheme is 7.56 dB away from its capacity curve, while it had a reduced gap as low as 2.25 dB, when using a longer TC block length of 40 000 modulated symbols. Finally, as a novel application example, the soft-decision M-DAPSK scheme was incorporated into an Amplify-and-Forward (AF) based cooperative communication system, which attains another 4.5 dB SNR improvement for a TC block length of 40 000 modulated symbols

Dispensing with channel estimation: differentially modulated cooperative wireless communications

As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective

Performance Analysis of Differential Beamforming in Decentralized Networks

This paper proposes and analyzes a novel differential distributed beamforming strategy for decentralized two-way relay networks. In our strategy, the phases of the received signals at all relays are synchronized without requiring channel feedback or training symbols. Bit error rate (BER) expressions of the proposed strategy are provided for coherent and differential M-PSK modulation. Upper bounds, lower bounds, and simple approximations of the BER are also derived. Based on the theoretical and simulated BER performance, the proposed strategy offers a high system performance and low decoding complexity and delay without requiring channel state information at any transmitting or receiving antenna. Furthermore, the simple approximation of the BER upper bound shows that the proposed strategy enjoys the full diversity gain which is equal to the number of transmitting antennas

Differential Modulation for Short Packet Transmission in URLLC

One key feature of ultra-reliable low-latency communications (URLLC) in 5G is to support short packet transmission (SPT). However, the pilot overhead in SPT for channel estimation is relatively high, especially in high Doppler environments. In this paper, we advocate the adoption of differential modulation to support ultra-low latency services, which can ease the channel estimation burden and reduce the power and bandwidth overhead incurred in traditional coherent modulation schemes. Specifically, we consider a multi-connectivity (MC) scheme employing differential modulation to enable URLLC services. The popular selection combining and maximal ratio combining schemes are respectively applied to explore the diversity gain in the MC scheme. A first-order autoregressive model is further utilized to characterize the time-varying nature of the channel. Theoretically, the maximum achievable rate and minimum achievable block error rate under ergodic fading channels with PSK inputs and perfect CSI are first derived by using the non-asymptotic information-theoretic bounds. The performance of SPT with differential modulation and MC schemes is then analysed by characterizing the effect of differential modulation and time-varying channels as a reduction in the effective SNR. Simulation results show that differential modulation does offer a significant advantage over the pilot-assisted coherent scheme for SPT, especially in high Doppler environments.Comment: 15 pages, 9 figure

WIRELESS NETWORK COCAST: COOPERATIVE COMMUNICATIONS WITH SPACE-TIME NETWORK CODING

Traditional cooperative communications can greatly improve communication performance. However, transmissions from multiple relay nodes are challenging in practice. Single transmissions using time-division multiple access cause large transmission delay, but simultaneous transmissions from two or more nodes using frequency-division multiple access (FDMA), code-division multiple access (CDMA), or distributed space-time codes are associated with the issues of imperfect frequency and timing synchronization due to the asynchronous nature of cooperation. In this dissertation, we propose a novel concept of wireless network cocast (WNC) and develop its associated space-time network codes (STNCs) to overcome the foretold issues. In WNC networks, each node is allocated a time slot for its transmission and thus the issues of imperfect synchronization are eliminated. To reduce the large transmission delay, each relay node forms a unique signal, a combination of the overheard information, and transmits it to the intended destination. The combining functions at relay nodes form a STNC that ensures full spatial diversity for the transmitted information as in traditional cooperative communications. Various traditional combining techniques are utilized to design the STNCs, including FDMA-like and CDMA-like techniques and transform-based techniques with the use of Hadamard and Vandermonde matrices. However, a major distinction is that the combination of information from different sources happens within a relay node instead of through the air as in traditional cooperative communications. We consider a general case of multiuser relay wireless networks, where user nodes transmit and receive their information to and from a common base node with the assistance from relay nodes. We then apply the STNCs to multiuser cooperative networks, in which the user nodes are also relay nodes helping each other in their transmission. Since the cooperative nodes are distributed around the network, the node locations can be an important aspect of designing a STNC. Therefore, we propose a location-aware WNC scheme to reduce the aggregate transmit power and achieve even power distribution among the user nodes in the network. WNC networks and its associated STNCs provide spatial diversity to dramatically reduce the required transmit power. However, due to the additional processing power in receiving and retransmitting each other's information, not all nodes and WNC networks result in energy efficiency. Therefore, we first examine the power consumption in WNC networks. We then offer a TDMA-based merge process based on coalitional formation games to orderly and efficiently form cooperative groups in WNC networks. The proposed merge process substantially reduces the network power consumption and improves the network lifetime

Multiple Symbol Double Differential Transmission for Amplify-and-Forward Cooperative Diversity Networks in Time-Varying Channel

In the cooperative diversity wireless networks, the task to perform cooperation communication amongst neighbouring nodes is very challenging. Subjected to rapidly increasing mobility of the nodes i.e. wireless devices in fast moving vehicles and trains, at the destination end the receiver may not ideally estimate the channel characteristics and frequency offsets. Due to these circumstances which results in time-varying channels, the performance network degrades drastically. In order to enhance the performance in such environment, Double Differential (DD) modulation employing multiple symbol based detection is proposed which takes mobility environment of different nodes into consideration. By utilizing the DD transmission approach, the channel properties and frequency offset estimation is omitted in the amplify-andforward cooperative networks. The MATLAB simulation and numerical analysis on Bit Error Rate (BER) are carried out with consideration on considering flat-fading (i.e. the frequency non-selective) Rayleigh channels and when frequency offsets. The results depict that the proposed method over fading channels without channel estimation requirements and in the presence of frequency offsets performs better as compared to the conventional DD transmission. Optimized power allocation is also carried out to enhance the network performance by minimizing the BER analytical expression. It is demonstrated that the proposed power allocation scheme offers enhancement over the equally distributed power allocation approach