Buffer-aided multihop wireless communications

Abstract

In this thesis, we propose a suite of buffer-aided transmission schemes designed for a multihop link or for a three-node network by exploiting the characteristics of buffer-aided transmissions. Our objective is to improve the end-to-end BER, outage probability, throughput and energy dissipation.

Specifically, we firstly proposed and studied a buffer-aided multihop link (MHL), where all the relay nodes (RNs) are assumed to have buffers for temporarily storing their received packets. Hence, the RNs are operated under the so-called store-and-forward (SF) relaying scheme. As a benefit of storing packets at the RNs, during each time-slot (TS), the best hop having the highest signal-to-noise ratio (SNR) can be activated from the set of those hops that have packets awaiting transmission in the buffer. A packet is then transmitted over the best hop. This hop-selection procedure is reminiscent of selection (SC) diversity, which is referred to here as multi-hop diversity (MHD), when assuming that each hop experiences both propagation pathloss and independent identically distributed (i.i.d) flat Rayleigh fading. In order to make the channel activation practical, a MAC layer implementation is proposed and several closed-form formulas are derived for its characterization.

Then we studied the buffer-aided multihop link, when assuming that each hop experiences both propagation pathloss and independent non-identically distributed (i.n.i.d) at Nakagami-m fading. Both BPSK as well as M-ary quadrature amplitude modulation (MQAM) are employed. During each TS, the MHD scheme activates the specific hop's transmission, whose signal-to-noise ratio (SNR) cumulative distribution function (CDF) gives the highest ordinate value amongst all the available hops. The next packet is then transmitted over the selected hop. This CDF-aware MHD scheme is suitable for operation in the scenarios, where the different hops may have different length, hence resulting in different average SNRs, and/or experience different types of fading. This MHD scheme is also capable of achieving the maximum attainable diversity gain provided by the independent fading experienced by the different hops.

Then the benefits of adaptive modulation are exploited, where the number of bits transmitted in each TS is affected both by the channel quality and the buffer fullness. During each TS, the criterion used for activating a specific hop is that of transmitting the highest number of bits (packets). When more than one hops are capable of transmitting the same number of bits, the particular hop having the highest channel quality (reliability) is activated. Hence we refer to this regime as the Maximum Throughput Adaptive Rate Transmission (MTART) scheme. Additionally, a new MAC layer protocol is proposed for implementing our MTART management.

Finally, we propose and study a routing scheme, namely the Buffer-aided Opportunistic Routing (BOR) scheme, which combines the benefits both opportunistic routing and MHD transmission. It is conceived for the transmission of information in a Buffer-aided Three-node Network (B3NN) composed of a Source Node (SN), a buffer-aided Relay Node (RN) and a Destination Node (DN). When applying opportunistic routing, each packet is transmitted from SN to DN either directly or indirectly via a RN based on the instantaneous channel quality. When applying MHD transmission, the RN is capable of temporarily storing the received packets, which facilitates transmission over three links, namely the SR, RD and SD links. In this network, the three channels define a 3D channel probability space (CPS), which is divided into four regions representing the activation-region of the three channels and an outage region. Then the instantaneous channel quality values map to a specific point in this 3D channel space. The BOR scheme relies on the position of this point to select the most appropriate channel in the 3D CPS for its transmission.

In comparison to the benchmark schemes considered in the literature, the BER, the OP, throughput and/or energy dissipation of our proposed systems are significantly improved.

More information

Identifiers

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

Catalogue record

Export record