Abstract
In order to leverage the spectrum resources, several forms of wireless duplex have been introduced and investigated in recent years. In Partial Duplex (PD) schemes, part of the band is transmitted in Full-Duplex (FD) and the rest in Half-Duplex (HD); therefore, some transmitted symbols will be characterized, at the receiver, by high SNR (Signal-to-Noise Ratio) and others by low SNR because of the residual self-interference (SI) in the FD part. Combining properly the patterns of these high and low SNR symbols affects the performance of the encoding schemes used in the system; in order to overcome this issue, different encoding and allocation schemes can be adopted for achieving a satisfactory solution. This paper investigates the performance of Low-Density Parity-Check (LDPC), turbo, polar codes for wireless PD. Orthogonal Frequency Division Multiplexing (OFDM) is an efficient multicarrier modulation technique, used in 4G and in the upcoming 5G, and it can be exploited for realizing a proper symbol allocation according to the SNR on each subcarrier. In this context, performance of LDPC, polar, and turbo codes derived from existing specifications has been studied when the system faces a mixture of high and low SNRs on the bits and hence on the symbols coming from the same codeword and this unbalanced SNR distribution is known a-priori at the transmitter, a condition associated with a scheme in which part of the symbols is subject to FD interference.
Highlights
Wireless mobile generations face a strong demand of services with high data rates to increasing numbers of connected users
We remark that the significant difference between the PD scheme and other schemes is in the flexibility of the bandwidth overlapping, without constraints on pulse filtering; being the system based on multi-carrier transmission, the channel frequency selectivity can be exploited for allocating the symbols and the FD subcarriers according to the SNR conditions (Figure 5); this selective and block strategies have been proposed in [1] and Section 5 will provide more details about the exploitation of this opportunity integrated with the encoding and allocation process
In addition to the reference, random-based strategy, we are validating a different allocation denoted as a positioning strategy, introduced in [7] and adapted here to the multi-carrier transmission. This strategy follows from the specific structure of the Low-Density Parity-Check (LDPC) parity check matrix: the symbols coming from the left part of the codeword are allocated in the subcarriers that will be characterized by high SNR and all the symbols coming from the right part of the codeword in the subcarriers with lower SNR (FD), obviously according to the Partial Duplex Parameter (PDP) of the system
Summary
Wireless mobile generations face a strong demand of services with high data rates to increasing numbers of connected users. The objective is twofold: (i) increasing the transmission range and/or (ii) being able to operate with an SI canceler of lower performance and complexity since this is the most challenging component of an FD system This PD scheme, characterized by the flexible mixing of HD and FD portions, is different from other schemes based on hybrid approaches: in [2,3,4], a partial overlap model named as α-Duplex is proposed, applicable to single-carrier. We show the performance achieved by different strategies for allocating low and high SNR symbols coming from the codewords derived and adapted mainly by the 4G and 5G 3GPP standards.
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