Noncoherent successive relaying for multi-user wireless systems

Abstract

A noncoherent detection based successive relaying aided network (SRAN) is proposed and investigated in the context of a multi-user, multi-relay assisted scenario. The potentially excessive complexity of multiple-antenna based power-hungry channel estimation is avoided by replacing the classic coherent detection by multiple-symbol-based noncoherent detection. Then, as the benefit of forming a virtual antenna array (VAA) in a distributed fashion, the proposed cooperative network becomes capable of achieving a substantial spatial diversity gain in the uplink. Furthermore, the 50% throughput loss incurred by the conventional single relay-aided two-phase cooperative network, which is caused by the half-duplex transmit/receive constraint of practical transceivers is recovered by designing a spectral efficient successive relaying protocol. Hence the proposed noncoherent successive relaying aided multi-user wireless system becomes capable of significantly improving the system’s performance.

We demonstrate that multiple-symbol differential detection (MSDD) is capable of eliminating the error floor of the conventional differential detection (CDD), when experiencing severely timeselective Rayleigh fading associated with a high Doppler frequency, since the MSDD algorithm benefits from a higher time-diversity than CDD. However, this is achieved at a potentially excessive complexity, which is unaffordable in many practical applications. As a remedy, the sphere decoding principle is incorporated into the MSDD algorithm. The resultant multiple-symbol differential sphere detection (MSDSD) strikes an attractive trade-off between the achievable BER performance and the complexity imposed. In order to improve the energy-efficiency, the hard-decision-based MSDSD algorithm is further developed to its soft-decision-based version, namely to the soft-input soft-output MSDSD (SISO-MSDSD). Furthermore, for the sake of exploiting the benefits of cooperative communications, we devise a new multiple-path propagation-aided MSDSD algorithm as a beneficial variant of the conventional MSDSD algorithm, which is further developed to the relay-aided MSDSD algorithm.

However, relay-assisted transmissions increase the amount of interference imposed. Hence, in order to suppress the successive relaying induced interference, namely both the inter-relay interference (IRI) and the co-channel interference (CCI), we invoke the DS-CDMA multiple access technique. Consequently, a noncoherent successive relaying (NC-SR) aided cooperative DS-CDMA uplink is conceived, where the typical 50% half-duplex relaying induced throughput loss is converted to a potential user-load reduction for the DS-CDMA system, since the SRAN requires two - rather than a single - spreading codes for each user. First, the AF protocol is invoked for the successive AF relaying aided DS-CDMA uplink, where initially a simple single-user scenario and then a realistic multi-user scenario are investigated. The evaluation of the associated noncoherent discreteinput continuous-output memoryless channel (DCMC) capacity indicates that our AF based SRAN is capable of significantly outperforming both the conventional AF relaying and the single-link direct-transmission. Then, as a counterpart, the successive DF relaying aided DS-CDMA uplink is also conceived, where a multi-user scenario is considered. The noncoherent DCMC capacity of the DF based SRAN reveals that the DF based SRAN may outperform the AF based SRAN, especially in the low SNR region. Furthermore, a relay-aided SISO-MSDSD assisted three-stage iterative transceiver is designed for supporting the operation of the proposed DF based SRAN, which is capable of operating close to the system’s capacity, while halving the system complexity imposed by the conventional single-path SISO-MSDSD aided distributed turbo decoder.

As a further advance, we also consider a multi-user multi-relay DS-CDMA uplink. In order to efficiently organize the cooperation among the multiple nodes of this large-scale wireless network, we further develop the concept of adaptive network coded cooperation (ANCC) to its generalized version, namely to our “GANC” regime, which allows arbitrary channel coding schemes to serve as the cross-layer network coding, while still adapting to both network topology changes and to link failures. Upon incorporating the proposed GANC regime into the SRAN, we construct the GANC aided SRAN. In the spirit of the joint network-channel coding (JNCC) scheme, we devise a generalized iterative detection based three-stage transceiver architecture for the proposed GANC aided SRAN. The proposed transceiver is also adaptive to both network topology changes as well as to link failures. We demonstrate that combining two DF based SRANs and operating them under the proposed GANC regime is capable of attaining a significant power gain with respect to operating them independently, i.e. without any cooperative between them.

Employing the DS-CDMA technique for suppressing the successive relaying-induced interference may lead to a potential user-load reduction for the DS-CDMA system. In order to mitigate the interference without requiring any extra orthogonal channel resources, we proposed a new multiple-symbol differential interference suppression (MS-DIS) regime, which is a novel amalgam of the adaptive modified Newton algorithm and of our SISO-MSDSD algorithm. Consequently, a MS-DIS-assisted plus relay-aided SISO-MSDSD based three-stage concatenated turbo transceiver is designed, which is capable of efficiently suppressing the interference at the expense of imposing as little as 2% training overhead, despite experiencing severely time-selective Rayleigh fading associated with a high Doppler frequency.

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Identifiers

ORCID for L. Hanzo: orcid.org/0000-0002-2636-5214

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