Energy consumption is a critical concern for the 5G mobile operators. 5G NR network may have increased energy consumption compared to its predecessors as it aims to support a plethora of services demanding diverse QoS constraints and requiring deployment of radios at different frequency layers with potentially wider bandwidth and more antennas. Moreover, it is important for the operators to keep the operational expenses and carbon emissions as low as possible as well. At 3GPP, UE power saving has mainly been the focus from Rel 15 till Rel 17 and in Rel 18, a new study item has been introduced to investigate different network power saving techniques. In this paper, we first discuss why 5G NR poses unique challenges for energy consumption with respect to its predecessors. We aim to explore different potential techniques for network power savings via resource adaptation in time, frequency, spatial, and power domain. We also investigate power consumption based on energy consumption model adopted by 3GPP and provide energy efficiency - throughput trade-off analysis to identify which domain has the highest potential for power savings.

Adaptive link selection for buffer-aided relaying can provide significant performance gains compared to conventional relaying with fixed transmission schedule, when perfect channel state information (CSI) is available for link selection. However, in practice, link selection may have to be performed based on outdated CSI, because of infrequent feedback of CSI and/or feedback delay. In this paper, we study the effect of outdated CSI on the error rate performance of adaptive link selection for a three node decode-and-forward (DF) relay network with fixed-rate transmission. In particular, we propose two protocols for link selection based on whether the reliability of the CSI estimates is known or not. For both protocols, we provide a unified error-rate analysis in terms of a decision threshold β, which can be adjusted to maintain buffer stability, and derive asymptotic approximations, which reveal the diversity and coding gains. Since packet transmission delay is unavoidable for opportunistic link selection, we analyze the average delay and throughput considering both finite and infinite buffer size. The average delay and throughput are functions of the decision threshold β, which can be optimized to minimize the error rate while satisfying average delay and/or throughput constraints. Numerical results manifest that even with outdated CSI, adaptive link selection provides a significant coding gain advantage over conventional DF relaying. Furthermore, we show that a diversity gain of two can be achieved for perfect CSI and the optimum error rate can be approached with small delay and/or high throughput.

This paper investigates the cross-layer optimization of fast video delivery and caching for minimization of the overall video delivery time in a two-hop relaying network. The half-duplex relay nodes are equipped with both a cache and a buffer which facilitate joint scheduling of fetching and delivery to exploit the channel diversity for improving the overall delivery performance. The fast delivery control is formulated as a two-stage functional non-convex optimization problem. By exploiting the underlying convex and quasi-convex structures, the problem can be solved exactly and efficiently by the developed algorithm. Simulation results show that significant caching and buffering gains can be achieved with the proposed framework, which translates into a reduction of the overall video delivery time. Besides, a trade-off between caching and buffering gains is unveiled.

Recent studies have shown that buffer-aided relaying with adaptive link selection can provide significant performance gains compared to conventional relaying using a fixed transmission schedule. In this paper, we focus on error rate analysis of adaptive link selection for a three node decode-and-forward (DF) relay network with fixed-rate transmission. As in practice link selection may be performed based on outdated channel state information (CSI) because of a delay in the feedback link, we study the error rate performance for both perfect and outdated CSI. Since a packet transmission delay is unavoidable with opportunistic link selection, we provide a unified error-rate analysis in terms of a decision threshold β which can be adjusted to achieve buffer stability and a desired average system delay. We show that a diversity gain of two can be achieved for perfect CSI and the optimum BER can be approached even if only a small delay is tolerated.

In this paper, we study the application of bit-interleaved coded modulation (BICM) and orthogonal frequency division multiplexing (OFDM) to reap the benefits of wireless multiuser network coding in practical frequency-selective fading channels. We propose a mapping based symbol level network coding (SLNC) scheme for a cooperative diversity system comprising multiple sources, multiple relays, and one common destination. A simple cooperative maximum-ratio combining scheme is used at the destination and is shown to successfully exploit both the full spatial and the full frequency diversity offered by the channel for arbitrary numbers of sources, arbitrary numbers of relays, and arbitrary linear modulation schemes. To gain analytical insight for system design, we derive a closed-form upper bound for the asymptotic worst-case pairwise error probability (PEP) and obtain the diversity gain of the considered SLNC scheme for BICM-OFDM systems. These analytical results reveal the influence of the various system parameters, such as the number of sources, the free distance of the code, and the frequency diversity of the involved links, on performance. Furthermore, we propose two different relay selection schemes for the considered system: a) bulk selection, i.e., a single best relay is selected to transmit on all sub-carriers, and b) per-subcarrier selection, where a best relay is selected on each sub-carrier. Last but not least, we exploit the derived PEP expression for selecting a subset of sources from the set of active sources when the number of active sources is larger than the number of available orthogonal relay channels. We study the achievable diversity gain for the proposed relay and source subset selection schemes. Numerical results corroborate the derived diversity gain expressions and confirm the performance gains.

In this paper, we consider a multisource multirelay network where relays employ buffers to store the received user data packets before forwarding them to a common destination. The transmission schedule, i.e., when each source and each relay transmit, is not a priori fixed, but rather depends on the link qualities. In particular, we consider adaptive link selection and adaptive rate transmission for the considered network. For simple three node relay networks, it was shown before that buffer-aided relaying with adaptive link selection yields significant throughput gains compared to conventional relaying protocols using a fixed transmission schedule. In this work, we consider a general multisource multirelay framework where operations are more complex and analysis is more involved. First, we consider average sum rate maximization for adaptive rate transmission and derive an adaptive link selection policy which exploits the channel state information. As fairness is an important issue in multisource networks, we also consider max-min fairness constrained throughput optimization and derive the corresponding link selection policy. Numerical results show that the proposed link selection policies yield significantly higher throughputs compared to conventional relaying schemes where source and relay transmission schedules are a-priori fixed.

In this paper, we study a cooperative diversity scheme for wireless systems where the relay is equipped with a buffer. We consider practical frequency—selective channels and adopt the combination of bit interleaved coded modulation and orthogonal frequency division multiplexing (BICM—OFDM). We propose a novel link selection protocol for BICM—OFDM systems where the relay either transmits or receives in a given time slot depending on the quality of the links. We derive a closed—form upper bound for the asymptotic worst—case pairwise error probability (PEP) and the diversity gain of the considered buffer—aided relaying scheme for both infinite and finite buffer size. We show that significant diversity gains can be achieved with buffer—aided relaying compared to conventional relaying at the expense of larger packet delays. In fact, for buffers of infinite (or very large) size, the diversity gain is doubled for links with identical frequency diversity, and an even higher diversity gain advantage is possible for links with non—identical frequency diversities. Furthermore, we perform an exact closed—form average delay analysis for buffers of both finite and infinite size which provides important insight into the achieved delay—performance tradeoff. The derived analytical results and performance gains are corroborated by extensive simulation results.

In this paper, we study a cooperative diversity scheme for wireless systems where the relay is equipped with a buffer. We consider practical frequency-selective channels and adopt the combination of bit interleaved coded modulation and orthogonal frequency division multiplexing (BICM-OFDM). We propose a novel link selection protocol for BICM-OFDM systems where the relay either transmits or receives in a given time slot depending on the quality of the links. We derive closed-form upper bounds for the asymptotic worst-case pairwise error probability and the diversity gain of the considered buffer-aided relaying scheme for infinite buffer size. We show that impressive diversity gains can be achieved with buffer-aided relaying compared to conventional relaying at the expense of packet delay. In fact, for buffers of infinite (or very large) size, the diversity gain is doubled for links with identical frequency diversity, and even a higher diversity gain advantage is possible for non-identical diversity links. The derived analytical results and performance gains are corroborated by simulation results, where we also show that for buffers of moderate size, a significant coding gain can be achieved, if not any diversity gain.

Coded cooperation is an attractive user cooperation scheme for wireless systems, where different parts of a coded packet are transmitted over different channels. In this paper, we propose a new approach to improve the performance of coded cooperation. We present cooperative maximum-ratio combining (C-MRC) based coded cooperation to guarantee full diversity even if the inter-user link is not ideal. Moreover, we combine bit-interleaved coded modulation (BICM) with orthogonal frequency division multiplexing (OFDM) to overcome frequency-selective fading. Taking possible decision errors at the cooperating sources into account, we develop a closed-form upper bound on the asymptotic worst-case pairwise error probability (PEP) of the considered C-MRC based coded cooperation scheme and obtain the diversity gain as function of free distance of the code and frequency diversity of the links. Furthermore, we discuss the optimization of the puncturing pattern based on the frequency diversity of the involved links. Simulation results corroborate the derived analytical results.

In this paper, we study a cooperative diversity scheme for wireless systems employing network coding and the combination of bit-interleaved coded modulation (BICM) and orthogonal frequency division multiplexing (OFDM). The considered system comprises multiple sources, one relay, and one destination. The relay decodes the signal received from all sources and performs network coding before forwarding the signal to the destination. We propose a simple cooperative maximum-ratio combining scheme for the destination which can successfully exploit the full spatial and frequency diversity offered by the channel for arbitrary numbers of sources and arbitrary linear modulation schemes. Furthermore, we propose techniques to reduce the signaling overhead and the decoding complexity at the destination. To gain insight for system design, we derive a closed-form upper bound for the asymptotic worst-case pairwise error probability and the diversity gain of the considered network coded cooperative BICM-OFDM system. These analytical results reveal the influence of various system parameters, including the number of sources, the free distance of the code, and the frequency diversity of the involved links, on performance. Based on the derived analytical results, we develop schemes for optimal relay placement and power allocation. Simulation results corroborate the derived analytical results and confirm the effectiveness of the developed optimization framework.

In this paper, we study a cooperative diversity scheme for wireless systems employing network coding and the combination of bit-interleaved coded modulation (BICM) and orthogonal frequency division multiplexing (OFDM). The considered system comprises multiple sources, one relay, and one destination. The relay decodes the signal received from all sources and performs network coding before forwarding the signal to the destination. We propose a simple cooperative maximum-ratio combining scheme for decoding at the destination which can successfully exploit the full spatial and frequency diversity offered by the channel for arbitrary number of sources and arbitrary modulation schemes. We derive a closed-form upper bound for the asymptotic worst-case pairwise error probability and the diversity gain of the considered network coded cooperative BICM-OFDM scheme. Simulation results corroborate the derived diversity gain and show the effectiveness of a low complexity decoding scheme.

In this paper, we study a decode-and-forward cooperative diversity scheme for wireless systems using the combination of bit-interleaved coded modulation (BICM) and orthogonal frequency division multiplexing (OFDM). We propose a simple cooperative maximum-ratio combining scheme for the destination which can successfully exploit the full spatial and frequency diversity offered by the channel. Taking possible decision errors at the relay into account, we develop a closed- form upper bound on the asymptotic worst-case pairwise error probability (PEP) of the considered cooperative diversity system which provides insight into the influence of various code and channel parameters on performance. The PEP expression is then exploited for optimal relay placement. Simulation results corroborate the derived analytical results regarding the diversity gain of the system and confirm the effectiveness of the proposed relay placement scheme.

This paper addresses the problem of speech dereverberation considering a noisy and slowly time-varying environment. The proposed multimicrophone speech dereverberation model utilizes the estimated acoustic impulse responses (AIRs) to dereverberate the speech as well as improve the signal-to-noise ratio without a priori information about the AIRs, location of the source and microphones, or statistical properties of the speech/noise, which are some common assumptions in the related literature. The received noisy signals are filtered through an eigenfilter which improves the power of the speech signal as compared to that of the additive noise. The eigenfilter is efficiently computed avoiding the tedious Cholesky decomposition, solely from the estimates of the AIRs. The design of the eigenfilter also incorporates a frequency domain constraint that improves the quality of the speech signal, resists spectral nulls in addition to improving the signal-to-noise ratio (SNR). A zero-forcing equalizer (ZFE) is used to dereverberate the speech signal by eliminating the distortion caused by the AIRs as well as the eigenfilter. The ZFE is implemented in block-adaptive form which makes the proposed technique suitable for speech dereverberation in a time-varying condition. The simulation results verify the superior performance of the proposed method as compared to the state-of-the-art dereverberation techniques in terms of log-likelihood ratio (LLR), segSNR, weighted spectral slope (WSS), and perceptual evaluation of speech quality (PESQ).

In this paper, we propose a novel cooperative diversity scheme for wireless systems employing the combination of bit-interleaved coded modulation (BICM) and orthogonal frequency division multiplexing (OFDM). The proposed scheme utilizes an amplify-and-forward protocol where relays are assigned to multiple groups. Relays in the same group transmit concurrently over disjoint sets of sub-carriers and relays in different groups transmit in different time slots. We derive closed-form expressions for the asymptotic worst-case pairwise error probability and the diversity gain of the proposed cooperative BICM-OFDM scheme. Based on the derived analytical results we develop design guidelines for sub-carrier allocation, relay grouping, and relay selection. Simulation results corroborate the derived analytical results and confirm the effectiveness of the developed optimization framework.

In this paper, we propose a novel amplify-and- forward cooperative diversity scheme for wireless systems using the combination of bit-interleaved coded modulation (BICM) and orthogonal frequency division multiplexing (OFDM). In the proposed scheme, multiple relays transmit concurrently over disjoint sets of sub-carriers. A careful joint design of the sub- carrier allocation at the relays and the interleaver at the source ensures that the proposed scheme can exploit the maximum spatial and frequency diversity offered by the wireless channel. An upper bound on the asymptotic worst-case pairwise error probability of the proposed cooperative diversity scheme is developed which provides insight into to the influence of various code and channel parameters on performance. Simulation results corroborate the analytical results regarding the diversity gain of the system and confirm the effectiveness of a newly developed relay selection criterion.

In this paper, we propose an improved eigenfilter design method for time domain equalizer (TEQ) design for discrete multitone (DMT) systems. In conventional DMT systems, TEQs used tend to introduce spectral nulls which degrade the achievable signal-to-noise ratio at the corresponding subcarriers. As a result, bandwidth efficiency decreases. Tkacenko and Vaidyanathan recently proposed a low-complexity eigenfilter method which though performs nearly optimally in terms of observed bit rate but suffers performance loss due to spectral attenuation. We present a joint cost function which, along with good channel shortening, avoids spectral nulls in the useful signal band. Simulation results show that our method allows more subcarriers to carry bits and thus outperforms conventional eigenfilter method in terms of achievable bit rate. We also propose a heuristic choice of optimal transmission delay which yields profitable bit rate performance.