Scalar quantization and probabilistic shaping are applied to the distributed source coding of Gaussian sources, with mean-square error distortion. A coding scheme with a modulo interval, dithering, and truncated Gaussian shaping is shown to achieve the corner points of the Berger-Tung region. The theory is illustrated by designing short-block-length multilevel 5G polar codes for Wyner-Ziv (WZ) polar coded quantization (PCQ). WZ-PCQ substantially reduces the total distortion compared to separate PCQ of the source blocks.

Scalar lattice quantization with a modulo operator, dithering, and probabilistic shaping is applied to the Wyner-Ziv (WZ) problem with a Gaussian source and mean square error distortion. The method achieves the WZ rate-distortion pairs. The analysis is similar to that for dirty paper coding but requires additional steps to bound the distortion because the modulo shift is correlated with the source noise. The results extend to vector sources by reverse waterfilling on the spectrum of the covariance matrix of the source noise. Simulations with short polar codes illustrate the performance and compare with scalar quantizers and polar coded quantization without dithering.

A coding scheme with scalar lattices is applied to K-receiver, Gaussian, vector broadcast channels with K independent messages, one for each receiver. The method decomposes each receiver channel into parallel scalar channels with known interference and applies dirty paper coding with a modulo interval, amplitude shift keying (ASK), and probabilistic shaping to each scalar channel. The achievable rate tuples include all points inside the capacity region by choosing truncated Gaussian shaping, large ASK alphabets, and large modulo intervals.

In this paper, we consider a joint sensing and communication (JSC) network in which multiple base stations (BSs) cooperate through a fusion center (FC) to detect and track the objects present in a supervised area. Every BS acts as a monostatic sensor capable of scanning the environment and sensing the targets while simultaneously communicating with user equipments (UEs). In particular, each BS generates range-angle maps, which are shared with a FC for data fusion and tracking via particle filter (PF) and multi-hypothesis tracker (MHT) algorithms. The performance of the proposed solutions is evaluated by varying the fraction of power and time devoted to sensing to manage the network overhead and offer a sensing/communication trade-off. Numerical results show that the proposed algorithms can successfully track multiple targets with different sizes and behavior in a vehicular scenario, ensuring, e.g., a root mean squared error (RMSE) of the estimated position of a pedestrian less than 50 cm when considering three BSs.

The use of 1-bit digital-to-analog converters (DACs) is a promising way to improve the energy efficiency of massive multiple-input-multiple-output (MIMO) systems. Many linear and nonlinear precoding techniques mitigating the severe quantization distortions have been introduced in order to enable the use of 1-bit DACs in the massive MIMO downlink. However, the vast majority of the proposed designs do not account for the channel strength imbalances between the users, which are highly likely to occur in the downlink scenarios. To achieve high sum rates in such scenarios, a user-specific power allocation scheme (USPA) is needed. In this paper, we propose a quantization aware USPA technique for the linear zero-forcing (ZF) precoder. Numerical results illustrate that higher achievable sum rates than the existing linear methods can be achieved with the proposed method, especially in the systems with low order modulated inputs. In the systems with higher modulation, the proposed method achieves similar performance to the existing methods, yet with a lower computational complexity.

In this work, we consider a multistatic joint sensing and communication network composed of a transmitter and multiple receivers capable of estimating the position of a target in the monitored area. In particular, the system consists of a transmitter equipped with multiple antennas (typically a base station) and several receivers that can act as sensors with a single antenna. The transmitter adopts multiple beams to accommodate the communication towards the user equipment and the sensing functionality, with the ability to split the power between the two beams to adjust the sensing/communication trade-off. Processing of target echoes by the sensors produces a bistatic distance estimate or soft maps, which are combined by the fusion center. We then propose two sensor data fusion strategies, least square and soft maps fusion; the former has a negligible impact on the network overhead, while the latter always provides better performance in terms of root mean squared error of target position estimation when considering a small fraction of power devoted to sensing. Finally, we highlight the benefits of cooperation offered by the multistatic configuration, compared to the bistatic one, in terms of power saving for sensing.

Many linear and nonlinear precoding techniques have been proposed to tackle the quantization distortions in the multiple-input-multiple-output (MIMO) downlink system deployed with 1-bit digital-to-analog converters (DACs). Very few of these techniques can support adequate sum rates in a realistic scenario with channel strength imbalances between the users. Higher sum rates can be achieved through a power allocation scheme which takes the 1-bit quantization distortions into account. In this paper, we propose a quantization aware sum rate maximizing power allocation algorithm for the regularized zero-forcing (RZF) precoder based on the asymptotic analysis. Numerical results illustrate that the proposed method achieves higher sum rates than the other state-of-the-art quantization aware sum rate maximization schemes.

Millimeter wave (mmWave) massive multiple-input-multiple-output (mMIMO) is a key technology for high capacity mobile communications. The straightforward implementation of mMIMO with fully digital precoding (FDP) and high resolution digital-to-analog converters (DACs) ends up with poor energy efficiency (EE) at the transmitter. Use of 1-bit DACs is a promising approach to improve the EE, since the power amplifiers (PAs) are driven with the maximum efficiency when they are fed with constant envelope (CE) signals. In this paper, we evaluate spectral efficiency (SE) and EE performances of FDP and hybrid precoding (HP) in mmWave mMIMO downlink to identify the more compatible option with the 1-bit quantization. Numerical results illustrate that FDP in general achieves higher SE and has higher EE at high signal-to-noise ratio (SNR), whereas HP has higher EE and achieves higher maximum EE at low SNR.

In this work, we analyze a probabilistic shaping based dirty paper coding (DPC) scheme on a two user multiple input single output (MISO) broadcast channel (BC) and evaluate rate region of the users in the finite block length regime by utilizing analytic approximations introduced for shaping and channel coding parts of DPC. The DPC scheme can be implemented with low complexity and enlarges rate region of the users in finite block length regime substantially compared to linear precoding and time sharing strategies.

Systems that combine sensing and communication functionalities are gaining interest for several possible applications related to the internet of things (IoT) and the upcoming 6G mobile radio networks. Studies have recently been proposed to find the optimal tradeoff between sensing and communication performance. However, these studies assume continuous transmission and thus consider that the time available for estimation can always be large enough to achieve some desired accuracy. Moreover, in line with this assumption, communication performance is measured via the well-known Shannon capacity, which implicitly assumes indefinitely long error correction codes. However, in the case of short packet transmissions, such as the case in several IoT applications, the above assumption is unrealistic, as the length of the transmitted packet limits that of the error correction code and the observation time for parameter estimation. Therefore, this paper aims at investigating the optimal tradeoff between the data transmission and the target localization capabilities in a finite block-length regime, by making use of some typical metrics of the finite length information theory. In particular, the optimal beamforming, which minimizes the Cramér Rao bound of target localization, is derived under a constraint over the block error probability for given packet length values.

Many common instances of power control problems for cellular and cell-free massive MIMO networks can be interpreted as max-min utility optimization problems involving affine interference mappings and polyhedral constraints. We show that these problems admit a closed-form solution which depends on the spectral radius of known matrices. In contrast, previous solutions in the literature have been indirectly obtained using iterative algorithms based on the bisection method, or on fixed-point iterations. Furthermore, we also show an asymptotically tight bound for the optimal utility, which in turn provides a simple rule of thumb for evaluating whether the network is operating in the noise or interference limited regime. We finally illustrate our results by focusing on classical max-min fair power control for cell-free massive MIMO networks.

Employing 1-bit quantization in massive multiple-input-multiple-output (MIMO) systems is a promising approach to improve the power efficiency. Various linear and nonlinear precoding techniques including the maximum safety margin (MSM) precoder have been presented to cope with severe 1-bit quantization distortions. In this paper, we show the reason for MSM precoder's success in reducing the quantization distortions and propose a low complexity extension with a greedy algorithm by exploiting this analytic result. Numerical results illustrate that the extended MSM is almost optimal in terms of maximizing the constructive interference (CI) between the received signals.

We consider the pilot signal for time (difference) of arrival (ToA, TDoA) estimation in an orthogonal frequency division multiplexing system with a cyclic prefix (CP-OFDM). The Cramér-Rao and Ziv-Zakai lower bounds are used to assess the performance of different pilot signals, under the assumption that the delay is distributed uniformly within a certain range. We adapt the analysis from previous works that have analyzed the performance of waveforms in an AWGN channel, but have not considered CP-OFDM. We find that in a CP-OFDM system, the ZZLB of the estimate depends only on the power allocation on the subcarriers, but not on their phase, if the pilot symbol is detected with an uncertainty up to the duration of the CP prior to the T(D)oA estimation and the CP is dropped at the receiver. This simplifies pilot signal design. Numerical results for Dirac-rectangular and triangular power allocations show that the performance follows a similar trend as for (single carrier) waveforms with a Dirac-rectangular and triangular power spectral density. But for a small uncertainty in the delay and a small number of allocated subcarriers, there is no transition region and it is optimal to allocate the pilot signals to the edge subcarriers.

In this paper, we consider the transmit and receive antenna array gain of massive MIMO systems. In particular, we look at their dependence on the number of antennas in the array, and the antenna spacing for uniform linear and uniform circular arrays. It is known that the transmit array gain saturates at a certain antenna spacing, but the receive array gain had not been considered. With our physically consistent analysis based on the Multiport Communication Theory, we show that the receive array gain does not saturate, but that there is a peak at a certain antenna spacing when there is no decoupling network at the receiver. As implementing a decoupling network for massive MIMO would be almost impossible, this is a reasonable assumption. Furthermore, we analyze how the array gain changes depending on the antenna spacing and the size of the antenna array and derive design recommendations.

We consider the reciprocity of the information-theoretic channel of Time Division Duplex (TDD) Multi-User-Multiple Input Multiple Output (MU-MIMO) systems in the up- and downlink. Specifically, we assume that the transmit and receive chains are reciprocal. We take the mutual coupling between the antenna elements at the base station and at the mobiles into account. Mutual coupling influences how to calculate transmit power and noise covariance. The analysis is based on the Multiport Communication Theory, which ensures that the information-theoretic model is consistent with physics. It also includes a detailed noise model. We show that due to the coupling, the information-theoretic up- and downlink channels do not fulfill the ordinary reciprocity relation, even if the input-output relation of the transmit voltage sources and the receive load voltages, i.e., the channel which is estimated with the help of pilot signals in the uplink, is reciprocal. This is a fundamental effect that is not considered otherwise. We show via Monte Carlo simulations that both, using the ordinary reciprocity relation, and not taking the coupling into account, significantly decreases the ergodic rates in single-user and the ergodic sum rates in multi-user systems.

A distribution matcher (DM) encodes a binary input data sequence into a sequence of symbols with a desired target probability distribution. Several DMs, including shell mapping and constant- composition distribution matcher (CCDM), have been successfully employed for signal shaping, e.g., in optical-fiber or 5G. The CCDM, like many other DMs, is typically implemented by arithmetic coding (AC). In this work we implement AC based DMs using finite-precision arithmetic (FPA). An analysis of the implementation shows that FPA results in a rate-loss that shrinks exponentially with the number of precision bits. Moreover, a relationship between the CCDM rate and the number of precision bits is derived.

Multiple works that address training and pre-coding in FDD massive MIMO systems are based on the assumption that the base station (BS) has a priori knowledge of the users' downlink (DL) channel covariance matrices. It is already known that columns of DFT (resp. Kronecker product of DFT) matrices approximate covariance eigen-vectors of large uniform linear (resp. rectangular) arrays in the large system limit. Therefore, DFT-based codebooks can be used for covariance eigenvector feedback from the user to the BS in FDD mode for the aforementioned arrays. It is not known, however, how much feedback is required, i.e., how many eigenvectors need to be fed back to the BS for a given DL signal-to-noise-ratio (SNR). The main paper contribution is discussing how the number of fed back covariance eigenvectors should be adapted to the DL SNR to achieve increasing sum rates with increasing SNR, and further discussing the feedback implications on training design. Numerical results scheme show only negligible sum rate losses compared to the case with perfect covariance knowledge at the BS.

Next-generation wireless systems will provide services requiring accurate position information of mobile users, as e.g. in vehicular and industrial communication scenarios. Accuracy in the order of tens of centimeters will be required, which cannot be provided by standard radio positioning techniques used in legacy systems. This work proposes a method for combining multiple radio signals, e.g. in aggregated carrier components or multiple radio interfaces, in such way that reference symbols transmitted therein can be used for a joint estimation of radio signals' time of arrival. Analysis of the Cramer-Rao Lower Bound and its numerical evaluation using the Maximum-Likelihood estimator clearly show that, also depending on the total signal bandwidth and reference symbols' density, performance gains of above 10 dB can be achieved. Moreover, signal processing and practical receiver architectures are described, which consider tradeoffs between computational complexity, reference symbols overhead and performance gains.

A distribution matcher (DM) encodes a binary input data sequence into a sequence of symbols (codeword) with desired target probability distribution. The set of the output codewords constitutes a codebook (or code) of a DM. Constant-composition DM (CCDM) uses arithmetic coding to efficiently encode data into codewords from a constant-composition (CC) codebook. The CC constraint limits the size of the codebook, and hence the coding rate of the CCDM. The performance of CCDM degrades with decreasing output length. To improve the performance for short transmission blocks we present a class of multi-composition (MC) codes and an efficient arithmetic coding scheme for encoding and decoding. The resulting multi-composition DM (MCDM) is able to encode more data into distribution matched codewords than the CCDM and achieves lower KL divergence, especially for short block messages.

Recently, several shaping schemes have been proposed for optical and wireless communications. A shaping technique modifies the distribution of transmit symbols to approximate the capacity achieving input distribution, hence resulting in a shaping gain. In this work, probabilistic and geometric shaping techniques for wireless backhaul channel are evaluated based on their frame error rate performance using soft and hard decision decoding with LDPC codes from the WiMAX and DVB-S2 standards. For soft decision decoding, both probabilistic and geometric shaping methods show significant gain compared to transmission with uniformly distributed symbols. However, when low complexity hard decision decoding is employed, only probabilistic shaping schemes exhibit large gains.

A modification to 5G New Radio (NR) polar code is proposed, which improves the error correction performance with higher order modulation through probabilistic shaping. The presented scheme mainly re-uses existing hardware at the transmitter, and modifications at the receiver are small. Simulation results show that the presented approach can improve the performance by up to 1dB for 256-QAM on AWGN channels.

The availability of abundant spectrum makes millimeter wave (mm-wave) a prominent candidate technology for the next generation of cellular networks. Highly directional transmission is essential for the exploitation of mm-wave bands to compensate for high propagation loss. The directional transmission, nevertheless, necessitates a specific design for mm-wave initial cell discovery, as conventional omni-directional broadcasting may fail in delivering cell discovery information. To address this issue, this paper provides an analytical framework for mm-wave beamformed cell discovery based on an information-theoretic approach. Design options are compared considering four fundamental and representative broadcasting schemes to evaluate discovery latency and overhead. The schemes are then simulated under realistic system parameters. Analytical and simulation results reveal four key findings: 1) analog/hybrid beamforming performs as well as digital beamforming in terms of cell discovery latency; 2) single-beam exhaustive scan optimizes the latency and, however, leads to the overhead penalty; 3) multi-beam simultaneous scan can significantly reduce the overhead and provide the flexibility to achieve tradeoff between the latency and the overhead; and 4) the latency and the overhead are relatively insensitive to extreme low block error rates.

We evaluate two architectures for fixed length distribution matching. Distribution matching is essential for probabilistic amplitude shaping, a modulation scheme recently proposed for next generation wireless communications. The parallel architecture, called the bit-level distribution matcher (BL-DM) is compared with the symbol-level constant composition distribution matcher (CCDM). Simulation results confirm higher throughput of the BL-DM without performance loss compared to the symbol-level CCDM, when multiple processors can be used. For single core systems, the symbol-level CCDM achieves higher throughput. We also prove that when the output distributions of the BL-DM and the symbol-level CCDM are the same, i.e., they can be represented as a product of binary distributions, the BL-DM achieves lower or equal rate-loss.

Millimeter wave (mm-wave) communication is essential for the next generation cellular networks. To exploit mm-wave frequencies, directional transmissions have to be applied to compensate the high propagation loss. Due to directional transmissions, initial access procedure of mm-wave communication systems needs specific design compared to conventional networks operating at sub-6 GHz. This paper focuses on an important step in the initial access procedure, namely broadcast signaling design for cell discovery. An analysis of such design is conducted based on an information theoretical approach, where four fundamental beam patterns, which cover most of the design options, are compared. Their performances in terms of cell discovery latency and signaling overhead are analyzed. The analysis reveals three key findings: (i) the average cell discovery latency depends only on beam duration and frame length, if the entire beacon interval can be accommodated in one frame; (ii) for low latency, single beam exhaustive scanning provides the best performance, but results in high signaling overhead; (iii) simultaneous multi-beam scanning can significantly reduce the overhead, and provide the flexibility to achieve trade-off between latency and overhead. The analytical results are verified by extensive simulations.

Millimeter wave (mm-wave) frequencies provide orders of magnitude larger spectrum than current cellular allocations and allow usage of high dimensional antenna arrays for exploiting beamforming and spatial multiplexing. This paper addresses the problem of joint scheduling and radio resource allocation optimization in mm-wave heterogeneous networks where mm-wave small cells are densely deployed underlying the conventional homogeneous macro cells. Furthermore, mm-wave small cells operate in time division duplexing mode and share the same spectrum and air-interface for backhaul and access links. The scheme proposed in this paper can significantly enhance network throughput by exploiting space-division multiple access, i.e., allowing non-conflicting flows to be transmitted simultaneously. The optimization problem of maximizing network throughput is formulated as a mixed integer nonlinear programming problem. To find a practical solution, this is decomposed into three steps: concurrent transmission scheduling, time resource allocation, and power allocation. A maximum independent set based algorithm is developed for concurrent transmission scheduling to improve resource utilization efficiency with low computational complexity. Through extensive simulations, we demonstrate that the proposed algorithm achieves significant gain over benchmark schemes in terms of user throughput.

Direct device-to-device (D2D) communication is considered as a key technology and enabler for a multitude of new services in future fifth generation (5G) networks. Especially safety and emergency applications will require fast and reliable handover, seamless D2D connectivity and proper radio access to the cellular network. This paper proposes a novel handover scheme, which takes advantage of the D2D sidelink in order to assist the handover procedure, provide connectivity and maintain synchronization among multiple radio links. The scheme is in particular beneficial for cases including users with partial cellular coverage, for which standard handover is not possible, provides connectivity to out-of-coverage users and further assists them in accessing again the cellular network. In a network-controlled implementation the proposed scheme can be used for flexible handover, allowing multi-link coexistence and avoiding large delays of inter-cellular D2D. Sequence diagrams and procedure flow charts are provided for selected scenarios.

Accurate hardware calibration is necessary to achieve channel reciprocity and enable closed-loop MIMO operation in time-division-duplex mode. In this paper, a simple over-the-air procedure that efficiently estimates the base station (BS) hardware chains is presented. The procedure is to be performed between the BS and a dedicated user equipment (UE) experiencing a high signal-to-noise-ratio, and is based on a downlink (DL) and a following uplink (UL) signaling procedure. The UE first estimates the DL channel of each BS antenna and then sends, in the UL, normalized inverses of the estimated DL channels. In addition, the UE feeds back a set of normalization parameters to the BS. The obtained UL signals in addition to the normalization parameters allow for the estimation of the BS hardware chains and ensure channel reciprocity is achieved. Numerical results illustrate the performance of the proposed procedure when a zero-forcing precoder is used at the BS.

We investigate the evolution of line of sight (LOS) blockage over both time and space for vehicle-to-vehicle (V2V) channels. Using realistic vehicular mobility and building and foliage locations from maps, we first perform LOS blockage analysis to extract LOS probabilities in real cities and on highways for varying vehicular densities. Next, to model the time evolution of LOS blockage for V2V links, we employ a three- state discrete-time Markov chain comprised of the following states: i) LOS; ii) non-LOS due to static objects (e.g., buildings, trees, etc.); and iii) non-LOS due to mobile objects (vehicles). We obtain state transition probabilities based on the evolution of LOS blockage. Finally, we perform curve fitting and obtain a set of distance- dependent equations for both LOS and transition probabilities. These equations can be used to generate time-evolved V2V channel realizations for representative urban and highway environments. Our results can be used to perform highly efficient and accurate simulations without the need to employ complex geometry-based models for link evolution.

Direct device-to-device (D2D) communication is considered to be part of fifth generation (5G) networks, while embodying vehicle-to- anything (V2X) communication into the recently defined Long Term Evolution (LTE) sidelink is already on the way. Coexistence of in-band D2D and cellular transmissions requires time synchronization between multiple links to prevent from interference and avoid using longer cyclic prefix or guard bands. This paper proposes a synchronization solution enabling interference-free coexistence of inter-cellular sidelink and existing cellular links, also considering non- synchronized base stations. Multiple synchronization sources including base stations, Global Navigation Satellite System (GNSS) and mobile users are hierarchically combined and network-instructed synchronization avoids any misalignments. Out-of-coverage users can form or join existing mobile networks by deploying the proposed distributed algorithm, which is found to limit the residual average timing error to below 0.5 μs.

For time division duplex systems with increased bandwidth in 5G, the concept of self-contained transmission has been proposed. Aiming at reduced latency and more flexible resource allocation, this concept involves frequent uplink and downlink switching and relatively short transmission in both directions. In this work, we consider single OFDM symbol transmission within self-contained transmission time intervals. Focusing on OFDM with pulse shaping, we propose a pulse shape with smooth transients in the time domain. Performance evaluation shows that an OFDM system with the proposed pulse shape exhibits better robustness against both noise and self-interference in comparison to the OFDM system with cyclic prefix. From the implementation point of view, pulse shaping requires only small modification to the transceiver and negligible computational complexity increase.

The predominantly used channel reciprocity condition in time-division-duplex mode only holds in practical systems if the transmit and receive hardware chains at the base station (BS) and at the user equipments are perfectly calibrated. Otherwise, there is a mismatch between the uplink (UL) and downlink channel state information (CSI) that leads to performance degradations. In this paper, we consider a multi-user MIMO system with hardware calibration errors (CaEs) at the BS and derive robust Bayesian precoders that minimize inter-user interference using the UL CSI and CaEs statistics as side information. The proposed robust precoding outperforms conventional non-robust precoding, and its gains compared to non-robust precoding increase with increasing numbers of users and CaEs. Furthermore, robust precoding can be used to relax calibration requirements, which is a result of practical interest. Our approach is applicable to any number of BS antennas but is especially important for massive MIMO systems where larger CaEs might be expected.

Cell-edge users suffer from harsh interference due to cell range expansion in a heterogeneous network. An information theoretic approach, namely the joint decoding, can in principle achieve the sum-capacity, but practical implementation remains a challenge. For example, a rate splitting (RS) scheme is an optimal alterative for multiple access channels, but it is not optimal for interference channels. This motivates us to develop a new technique. In this paper, a practical scheme called multi-layer rate splitting (MLRS) is introduced. We prove that this MLRS scheme can achieve the sum capacity when the interference channel satisfies certain conditions. Moreover, a power allocation algorithm is proposed to find the optimal power splitting ratios for the MLRS scheme. Simulation results show that the MLRS scheme is an effective alternative to exploit the benefit of the joint decoding for interference channels.

Harsh interference is a major obstacle to achieve high capacity, especially when the state-of-the-art wireless networks intend to reuse the same resource. Information theoretic study shows that joint decoding with interference can achieve the sum capacity of a strong interference channel. However, the optimal joint decoding technique is too complex for practical applications, because it requires detecting and decoding all messages simultaneously. A two-user strong interference channel can be formed by two two- user multiple access channels (MACs), so a natural question arises as whether the decoding schemes optimal for the MAC remains optimal when applied to the interference channel. This paper investigates the relevant decoding techniques, namely the MAC rate splitting (RS) and iterative detection-decoding. Although these techniques have been shown to be optimal for MACs, we show that they cannot achieve the optimal performance anymore under interference channels.

With increasing importance of location based services, requirements for TOA (time of arrival) and TDOA (time difference of arrival) measurements have been specified in 3GPP LTE Rel. 9 to ensure accurate TIE (user equipment) positioning. In order to meet these requirements, it is vital to accurately estimate the first signal arriving path. This is, however, not trivial, especially in multipath environments. In this work, we describe methods for LTE TOA and TDOA measurements with enhanced first arriving path detection. The conventional maximum likelihood based correlation profile is used as detection metric. After grossly determining the signal region by a moving window, three methods, namely peak detection, SNR based threshold and adaptive threshold based on noise floor and metric peak value are employed to estimate the first arriving path. Simulations results show that the proposed adaptive threshold based method is robust against channel variations and can meet all 3GPP requirements under various multipath channels.

In wireless networks, interference from adjacent base stations is usually a dominant factor for user performance degradation. A maximum likelihood (ML) detection can provide superior performance by jointly detecting the serving and interfering signals. However, the complexity is extremely high. This paper presents a soft tree pruning based fixed-complexity sphere decoder. It uses reliability information on bits to estimate a search radius and thereby prunes unpromising nodes in the early stage of the tree search detection to reduce complexity. Based on the soft tree pruning method, the fixed-complexity sphere decoder can still work in a fully pipelined mode. Simulation results show that the soft tree pruning based fixed-complexity sphere decoder can provide a better trade-off between complexity and performance in interference-limited scenarios.

Quick detection and accurate measurement of multiple cells surrounding the user equipment (UE) are essential to ensure the mobility and QoS of end users. In LTE and LTE-A, multiple cells are often time synchronized or quasi-synchronized so that weak cells “eclipsed” by strong interfering cells are difficult to detect. In this study, we present a novel neighbor cell search and measurement method in which cross-correlation (e.g. of synchronization signals) is explicitly exploited. The basic idea is that the cell detection metric is modified according to the cross-correlation between the interfering cell and the cell to be detected and/or the signal power of the interfering cells such that the impact of the interferer is properly suppressed. Analysis and simulations show that the proposed method is simple to implement and robust against parameter mismatch, channel variation and RF impairments. Excellent results are obtained, especially in detecting the weak “eclipsed” cells.

Cell-edge users inevitably suffer from strong interference from adjacent cells, and consequently their throughput will decrease. Recent investigations show that the Han-Kobayashi (HK) rate splitting scheme is the best known strategy to mitigate the interference for a two-user interference channel. However, its receiver is too complicated to implement in practical systems. This paper takes the multi-layer rate splitting (MLRS) scheme as an alternative and proposes a new mutual-information based power allocation algorithm for the MLRS scheme. Simulation results for the scenarios of two cell-edge users show that the proposed power allocation algorithm brings two advantages. First, it can reduce the complexity of receivers for the MLRS scheme. Second, it can achieve performance comparable to the simple HK scheme in a two-user fading interference channel and provide about 39% gains in terms of average throughput, compared with a fixed frequency reuse 2 scheme, in a realistic tri-sectored wireless network.

In a multi-cell wireless network, cell-edge user equipments (UEs) inevitably suffer from strong interference from adjacent cells which leads to the UE throughput decrease. Contrary to conventional interference mitigation techniques which treat the interference as noise, we propose to use a rate splitting based interference exploitation technique. A novel distributed power allocation algorithm is adopted to optimize the performance. Simulation results show that the multi-layer rate splitting scheme with the proposed power allocation algorithm can approach the best known achievable rate bound of a two-user interference channel and substantially improve the performance of cell-edge UEs in a tri-sectored network.

In a multi-cell wireless network, an efficient interference mitigation technique is an inevitable part of the current state-of-the-art wireless system. As opposed to conventional interference mitigation techniques which treat the interference as noise, a multi-layer rate splitting scheme can be considered to improve the performance by decoding part of the interference. In this paper, we adapt the multi-layer rate splitting scheme to a Long Term Evolution Advanced framework. Simulation results for two UEs show that the proposed multi-layer rate splitting scheme substantially improves the performance of the cell-edge UE and achieves better fairness between the involved UEs.

Cell-edge users inevitably experience strong interference from adjacent cells, and consequently suffer from performance degradation. Currently, Han-Kobayashi (HK) rate splitting scheme is viewed as the best strategy to cancel the interference and improve the performance. As a special superposition coding scheme, the HK rate splitting scheme has been shown to potentially achieve the channel capacity. However, the way from theory to practice is not straightforward. Current investigations adapting the HK rate splitting scheme to practical applications only deal with the strongest interference and treat the other interferences as noise. In general, more than one strong interferer usually exists, which is targeted in this work. By applying a multi-layer rate splitting scheme for more than one strong interferer, a new ordered detection is proposed and a power allocation algorithm is derived associated with the detection order. Simulation results show that the multi-layer rate splitting scheme mitigates the interference from two different interferers and provides more than twice the gain in terms of average throughput compared with a reference scheme with a fixed frequency reuse factor of 3 in a realistic wireless network.

The Long Term Evolution (LTE) system, like other OFDM based systems, is very sensitive to synchronization errors which must be estimated and compensated. In this paper, maximum-likelihood (ML) estimates of the Carrier Frequency Offset (CFO) and Sampling Frequency Offset (SFO) are investigated in the framework of LTE downlink, aiming at precisely tracking time-varying fluctuations of the impairments. In order to make the tracking independent of the time index of the OFDM symbol, the differential CFO and SFO tracking algorithm are proposed. Combined with the phase ambiguity cancellation scheme, the differential tracking algorithm can work with high accuracy. The performances are analyzed and evaluated through simulations.

This paper addresses problems related to time and frequency synchronization as well as blind CP (cyclic prefix) type identification in 3GPP LTE system. We start with a general framework based on maximum likelihood (ML) parameter estimation. Then, simplified practical algorithms for estimating time and frequency offset as well as blind CP length are described. Finally, a robust hierarchical scheme is proposed. Specifically, the CP based lagged auto-correlation is first employed to identify the CP type, estimate the carrier frequency offset (CFO), and grossly determine the symbol timing, and then the pilot (i.e. the LTE primary synchronization signal) based cross-correlation is used to more accurately determine the symbol and frame timing. A solution is given to the problem with unequal-length symbols, such as the symbols with the normal CP specified in the LTE. The proposed hierarchical scheme has both low complexity and high accuracy and can be realized without hardware support.

Future digital subscriber line (DSL) systems are supposed to achieve higher data rates by using interference cancellation techniques. Since far-end crosstalk (FEXT) is the major impairment in DSL systems based on frequency division duplexing, mitigation of this interference can increase the signal- to-interference-and-noise ratio, and therefore significantly boost the data rate. For simulation and evaluation of FEXT cancellation algorithms, more accurate modelling of the multiple-input- multiple-output (MIMO) crosstalk channels is needed. Until now, DSL standards usually rely on the 99% worst case modelling of crosstalk power-sum for the lines in a binder. This paper proposes a parametric stochastic FEXT model based on the sum-of-sinusoids approach for the pair-to-pair crosstalk among multiple lines in a binder, which shows a more realistic behaviour than the worst case models.

In this paper we investigate the time and frequency synchronization as well as the sector and cell search for the 3GPP long term evolution (LTE) downlink. The proposed algorithms rely on the synchronization and cell-specific reference signals and are hence compliant to most recent 3GPP specifications. Time and (fractional) frequency offset coarse synchronization are performed in the time domain with the cyclic prefix based autocorrelation, while the sector and cell as well as the integer frequency offset are estimated in the frequency domain by using the primary and secondary synchronization signals. To improve the cell detection reliability, the estimated cell is afterwards confirmed through the cell-specific reference signal. All algorithms are evaluated under multipath channel conditions and an initial carrier frequency mismatch. Compromising high performance with reasonable implementation complexity, we draw a practical solution for an LTE receiver.

A multi-layer Interleave-division multiple access (IDMA) based system proposal is presented in order to enhance the universal terrestrial radio access (UTRA) uplink. Compatibility and co-existence with the current UTRA FDD mode are of primary importance. Although focus is on UTRA long term evolution and related research activities initiated by the 3rd generation partnership project (3GPP), multi-layer IDMA may be applied to enhance other direct-sequence code- division multiple access (DS-CDMA) systems, or may serve as an innovative air interface for future systems. As a novel feature, non-uniform power allocation on chip level is introduced.

Dynamic interactive multimedia scenes (DIMS) is the latest 3GPP multimedia standard aiming at the development and delivery of rich media services over mobile networks, specifically for the constrained devices. DIMS is a concept that encompasses a declarative format for audio-visual scene representation, as a composition of rich media objects with specific properties and behaviour. This paper focuses on the issues related to the delivery of Interactive TV like services with DIMS in mobile broadcast environments. We have investigated the system design parameters which would ensure better QoS for the subscribers. With the simulation results, we have setup guidelines for the selection of application layer FEC parameters, video coding settings and optimum base station transmit power. These guidelines assist in improving the overall rich media experience offered to the end-users.

Error robust video communication for hand-held devices is a delicate task because of limited computational resources and hostile channel conditions in mobile environments. The loss of coded video data on the channel can result in spatio-temporal error propagation in the video. In addition, stringent end-to-end delays for conversational applications make this challenge even more difficult. In this work, we investigate several techniques which exploit feedback from the receiver to enhance the performance of conversational video in realistic mobile communication environments. Specifically, we show how a low-complexity interactive error tracking technique can be combined with multiple reference picture selection (RPS) based on the existing syntax of H.264/AVC. This technique outperforms other interactive error protection strategies by a margin of more than 2 dB for moderate channel loss rates, with minimal impact on end-to-end delays.

Abstract The integration of reliable Video‐on‐Demand (VoD) broadcasting schemes in mobile datacast systems, specifically in DVB‐H, is studied and enhanced. Sophisticated VoD broadcasting schemes such as Harmonic Broadcasting (HB) allows receivers to tune into the ongoing transmission of a video stream at arbitrary time, while still being able to receive the multimedia sequence from beginning to end, after short initial playout latency. In addition, we address service enhancements by using scalable video coding (SVC) to support heterogeneous receiver capabilities and receiving conditions as well as the reception of the signal from more than on transmission site. We present and discuss options for the integration of VoD broadcasting schemes in combination with fountain codes. Optimizations in parameter selection are discussed. A realistic protocol environment is only slightly modified to support our system concept. Simulation results show the benefits of the discussed VoD scheme compared to existing approaches if integrated in DVB‐H. Copyright © 2007 John Wiley & Sons, Ltd.

Abstract — 3GPP has specified Multimedia Broadcast/Multicast Services (MBMS) addressing the increasing demands of multimedia download and streaming applications in mobile scenarios. Thereby, video coding is an essential component and H.264 is the only recommended video codec in MBMS mainly due to its high compression efficiency and easy network integration. In this paper we introduce the main system design parameters that influence the performance of MBMS video streaming over EG-PRS and UMTS using H.264 encoded streaming. Effective design methodology that includes robustness against packet losses and efficient use of the scarce radio resources is presented. Thereby, care is taken also about the limited processing power of mobile terminals, service delay constraints, and heterogeneous receiving conditions. We also investigate an advanced receiver concept, the so called permeable–layer receiver. Selected simulation results show the suitability of certain parameter settings as well as the benefits provided by the advanced receiver concept. I.

In this work we address reliablefile delivery over mobile broadcast networks, concentrating on the Raptor codes as specified for Multimedia Broadcast/Multicast Services (MBMS) within 3GPP. We start by describing Luby-Transform (LT) codes, which are the first practical fountain codes. Then, using a natural and easy to understand linear algebra notation, we describe Raptor codes as a powerful extension of LT codes. We provide some insight into the Raptor code structure and some guidelines for implementation of encoders and decoders. Finally, some selected simulations verify the good performance of file distribution with Raptor codes as specified in 3GPP. References to a complete set of simulation results are also provided. I. INTRODUCTION

Raptor codes have been recently standardized by 3GPP to be used in the application layer. These codes are very efficient and perform sufficiently close to the so-called ideal fountain code on the block-erasure channel. However, for real applications, a simple receiver enhancement called permeable layer receiver can be done, which provides huge performance gains. Standard Raptor decoding algorithms have to be revised and new efficient decoding algorithms need to be introduced. In this work we present a practical and efficient implementation of the Raptor decoder for permeable layer receiver. We show that, not only we achieve huge performance gains, but we achieve them at an affordable (low) decoding complexity. Complexity and decoding performance simulation results are presented for the download delivery and video broadcasting.

In this paper, a receiver structure suitable for single-antenna cochannel interference cancellation in cellular TDMA networks is studied. The receiver under investigation consists of a novel linear prefilter followed by a nonlinear detector. The task of the prefilter is to suppress non-Gaussian interference and - simultaneously - to shorten the overall impulse response, whereas the task of the nonlinear detector is to cancel intersymbol interference. The prefilter is designed according to the principle of minimum mean square error estimation, without solving an eigenvalue problem. Optionally the prefilter can be designed utilizing available knowledge of all cochannels, knowledge of the channel of a desired user only, or with no channel knowledge at all. The nonlinear detector may be an arbitrary nonlinear equalizer, in the simplest case a memoryless detector. The receiver structure under investigation is compatible with conventional TDMA receivers ignoring cochannel interference. Performance results are presented for synchronous and asynchronous GSM/GPRS networks

In 3GPP GERAN, the performance specification of dual-antenna interference suppression techniques will be a subject of the downlink advanced receiver performance (DARP) phase II work item. In this study, we apply a filter-based single antenna interference suppression technique for downlink GSM 8PSK modulation assuming the terminal is equipped with two antennas. We evaluate the performance using a correlation-based spatial channel model and show the potential of suppressing the co-channel interference even for high correlation factors. Besides, a performance improvement can be observed if the phase angles of the correlation factors for the desired user and interferer are different in highly spatially correlated channels

In this letter, single antenna co-channel interference cancellation for cellular time-division multiple access (TDMA) networks by means of joint delayed-decision feedback sequence estimation is studied. The performance is increased by a novel adaptive state allocation technique.

In this paper, a novel design of a receiver-side FIR prefilter is proposed which is able to jointly shorten the impulse responses of multiple co-channels given just one receive antenna. The prefilter coefficients are computed without explicitly solving an eigenvalue problem. In conjunction with a reduced-complexity multiuser detector, a good error performance can be achieved. As a possible application, co-channel interference cancellation for the EDGE system is studied. The prefilter, however, is also suitable for interference suppression in MIMO systems, for crosstalk suppression, or for reducing the length of the cyclic prefix in multitone systems, among other applications.

In this paper different means for adding reliability in different protocol layers are discussed, in order to reliably broadcast multimedia data within existing wireless networks. In particular, we investigate the performance of additional forward error correction in the physical layer, the radio link control layer, and the RTP layer for multimedia broadcast and multicast services over GERAN systems. Advantages and drawbacks when applying means for reliability in different layers are shown. We introduce a simple receiver modification, referred to as permeable-layer receiver (PLR), which exploits traditionally useless information at the receiver, while the transmitter is kept unchanged. Significant performance gains are reported. Finally, the application to H.264/AVC based wireless video broadcast is discussed and the performance of different system designs for video transmission is shown.

Various advanced methods have been proposed to achieve sufficiently high throughput as well as reliability for multimedia broadcast multicast services (MBMS) within 3GPP RAN and GERAN. One of the methods which yield promising results with only marginal system modifications is based on outer Reed-Solomon (RS) coding on the radio link control (RLC) layer. For initial studies standard decoding algorithms based on erasure-only decoders have been employed. In order to further improve the performance, the system can be viewed as a serially concatenated code such that iterative decoding can be performed. Then, advanced receivers for MBMS over GERAN would incorporate soft-in soft-cut (SISO) decoders for both the inner convolutional code, as well as the outer RS code. Whereas for the convolutional code, standard SISO algorithms are applied, for the outer RS code a standard Berlekamp-Massey algorithm is modified to accept soft-input and to provide soft-output. With this modified iterative decoding strategy, simulations have shown gains of up to 14% in throughput on typical mobile radio channels.

In this work, reliable retransmission strategies, including point-to-point (p-t-p), point-to-multipoint (p-t-M) and point-to-multipoint incremental redundancy (p-t-M-IR) are studied with special focus on their applicability to multimedia broadcast and multicast services (MBMS) over GERAN. By employing a binary OR multiple access channel (BORMAC) model, analytical expressions for the system throughput, the residual RLC/MAC block loss rate, and the residual IP-packet loss rate are derived for all investigated schemes. Furthermore, a simple NACK oriented feedback policy, which allows the utilization of a resource efficient feedback channel in cellular environments is presented. It is shown that the p-t-M-IR scheme outperforms both the p-t-p and the p-t-M retransmission scheme significantly in terms of system throughput, residual loss RLC/MAC block loss rate, as well as residual IP-packet loss rate. The throughput reduction of the p-t-M-IR scheme with increasing number of mobiles in the serving area is significantly less than with other ARQ schemes.

In this paper, forward error correction (FEC) on the application layer for reliable multicast transmission over wireless is investigated. A wireless channel model is introduced and analytical performance bounds for FEC on the application layer over wireless are given. It is shown that with state-of-the-art receiver strategies the residual application layer packet loss rate exceeds the required target loss rates and that sufficient quality-of-service (QoS) cannot be achieved. A simple receiver modification, called permeable-layer receiver (PLR), is introduced, which exploits traditionally useless information at the receiver, while the transmitter is kept unchanged. The PLR is shown to outperform the traditional receiver, allowing the efficient support of many wireless receivers in a multicast environment at the same time. Simulation results with LDGM staircase codes are provided, being consistent with theoretical findings. Future work items to support and extend the conceptual findings are discussed.

Single antenna co-channel interference cancellation for cellular TDMA networks by means of joint delayed-decision feedback sequence estimation is proposed. The performance can be increased by a novel adaptive state allocation technique.

We will present an algorithm for enhanced AMR mode switching for VoIP over GERAN that takes into account abstract criteria like frame delay and packet loss rate at the application layer, as well as segmentation overhead at the data link layer. With the proposed algorithm in a wireless terminal, dynamic cross-layer optimization between the VoIP application and the radio network control can be achieved even if the peer codec is situated far away from the air interface. The performance improvements of the algorithm will be demonstrated for a typical GERAN scenario in terms of achieved speech quality, as well as resource consumption and utilization efficiency at the air interface.