The growing complexity of urban transportation networks demands intelligent, data-driven systems capable of real-time perception, optimization, and prediction. Within the Internet of intelligent Vehicles (IoIV), optimal sensor placement is essential for enhancing distributed edge intelligence, as it significantly improves traffic observability, ensures accurate data collection, and enables dynamic decision-making. In this context, we propose a dual approach for hybrid quantum-classical (HQC) optimization—classical for quantum and quantum for classical. First, we formulate the optimal sensor placement problem within the quantum approximate optimization algorithm (QAOA) framework using a minimum vertex cover approach to address its NP-hard nature. Moreover, we enhance the QAOA by integrating long short-term memory (LSTM) networks to adaptively optimize its parameters, thereby achieving faster convergence and improved surveillance coverage in urban transport networks. Second, we employ quantum LSTM (QLSTM) networks to predict traffic flow from data collected by the optimally placed sensors. The QLSTM model reduces the number of learnable parameters while maintaining the expressive capability of classical LSTM architectures. This semantic information is then leveraged to manage traffic flow more effectively, predicting traffic patterns and supporting proactive decision-making. Experimental results demonstrate that the LSTM-guided QAOA outperforms conventional optimization methods such as stochastic gradient descent, achieving faster and more reliable convergence. Likewise, the QLSTM model attains superior predictive accuracy, as evidenced by significant improvements in the explained variance score and root mean squared error. Collectively, these advancements represent a substantial step forward in intelligent traffic management and highlight the practical potential of HQC machine intelligence in IoIV systems.

We consider utility maximization problems in the downlink cell-free massive multiple-input multiple-output (MIMO) whereby a large number of access points (APs) simultaneously serve a group of users. Four fundamental maximization objectives are of interest: (i) average spectral efficiency (SE), (ii) proportional fairness, (iii) harmonic-rate, and (iv) minimum SE of all users, subject to a sum power constraint at each AP. As considered problems are non-convex, existing solutions normally rely on successive convex approximation (SCA) and use off-the-shelf convex solvers, which implement an interior-point algorithm, to solve derived convex problems. The complexity of such methods scales quickly with the problem size. Therefore, we propose an accelerated projected gradient method to solve the considered problems. Particularly, each iteration of the proposed solution is given in a closed form and only requires the first order oracle of the objective, rather than the Hessian matrix as in known solutions, and thus is much more memory efficient. Numerical results demonstrate that our proposed solution achieves the same utility performance but with far less run-time, compared to the SCA method. Simulation results show that large-scale cell-free massive MIMO has the intrinsic user fairness, i.e. the four utility functions can deliver nearly uniformed services to all users.

The ultra‐dense network (UDN) has been identified as a promising solution to accommodate a tremendously increasing number of traffic. Clustering for small cell base stations is considered as an efficient frequency resource management scheme. In this study, the authors propose a flexible clustering algorithm to achieve traffic load balancing between clusters as well as reduced inter‐cell interference. They implement a malleable cluster configuration with cluster splitting and recombining. Simulation results demonstrate that the proposed clustering technique is useful and practical, providing high average throughput and lowering outage probability.

Coping with the limited amount of available spectrum, time division duplexing (TDD) system is considered as an attractive duplexing method due to exploiting channel reciprocity as well as flexible resource management. The conventional scheduling scheme is based on the channel quality indicator (CQI) reported from the user equipment (UE) to estimate instantaneous data rates for the scheduling metric calculation. However, CQI is insufficient to reflect the state of the channel variation in terms of frequency and time. Based on the channel reciprocity of TDD systems, we utilize uplink sounding reference signal (SRS) to estimate downlink channel status. However the received SRS power is a result of uplink power control where power control effect should be compensated to estimate channel status in downlink scheduling. In order to solve this problem, we propose the SRS path loss estimation method based on the power headroom report. By using this scheme, the base station (BS) can obtain the compensated signal-to-interference-plus-noise-ratio (SINR) and determine the scheduling metric based on its calculated SINR instead of reported CQI from UE. Simulation results show that the proposed scheduling algorithm outperforms the conventional scheme in total throughput, whereas the fairness index experienced by the proposed algorithm is lesser than of the conventional scheme based on CQI.

We consider small-cell networks with multiple-antenna transceivers and base stations (BSs) cooperating to jointly design linear precoders to maximize the network energy efficiency, subject to a sum power and per-antenna power constraints at individual BSs, as well as user-specific quality of service (QoS) requirements. Assuming zero-forcing precoding, we formulate the problem of interest as a concave-convex fractional program to which we proposed a centralized optimal solution based on the prevailing Dinkelbach algorithm. To facilitate distributed implementations, we transform the design problem into an equivalent convex program using Charnes-Cooper's transformation. Then, based on the framework of alternative direction method of multipliers (ADMM), we develop a decentralized algorithm, which is numerically shown to achieve fast convergence. Since BSs are generally power-hungry, it may be more energy-efficient if some BSs can be shut down, while still satisfying the QoS constraints. Toward this end, we investigate the problem of joint precoder design and BS selection, which is a mixed Boolean nonlinear program, and then provide an optimal solution by customizing the branch-and-bound method. For real-time applications, we propose a greedy algorithm which achieves near-optimal performance in polynomial time. Numerical results are provided to demonstrate the effectiveness of the proposed algorithms.

This paper proposes a hybrid double-threshold based energy detector (HDTED) for cooperative spectrum sensing over imperfect channels in cognitive wireless radio networks (CWRNs). The proposed HDTED improves the sensing reliability in CWRNs by exploiting both local decisions at secondary users (SUs) in either binary or energy values and global binary decisions feedback from fusion centre. Particularly, we consider a practical scenario where all channel links suffer from fading and noise. By deriving closed-form expressions and bounds for the probabilities of missed detection and false alarm, we not only show the improved performance achieved with the HDTED scheme but also validate the effects of the number of the SUs and the fading channels on the overall sensing performance.

A joint power splitting and beamforming design for multiuser multiple-input single-output (MISO) systems where receivers have capability of decoding information and harvesting energy simultaneously from received signals is considered. The objective is to maximize the ratio of the achieved utility to the total power consumption subject to harvested power requirements and power budget at a base station (BS). The utility function of interest combines the sum rate and the total harvested power. The design problem is nonconvex, and thus, global optimality is difficult to achieve. To solve this problem locally we first convert the problem into a more tractable form, and then propose an iterative algorithm which is guaranteed to achieve a Karush-Kuhn-Tucker solution. Numerical results are provided to demonstrate the superior performance of the proposed method.

This paper studies the problem of resource allocation for uplink multi-homing users in heterogeneous network where users can simultaneously transmit data to multiple radio access networks (RANs). The considered design problem is to optimally assign bandwidth and power to each user-RAN connection so as to maximize the overall energy efficiency of the network subject to QoS requirements and resource budgets. By the definition of energy efficiency which is the ratio of the aggregate throughput to the power consumption, the resulting problem is formulated as a fractional program. Then, we propose an energy efficient algorithm using the Dinkelback method that solves a series of convex problems to obtain the optimal design. Particularly, we derive closed-form expressions for the design parameters and provide useful insights into the proposed energy efficient resource allocation algorithm. Numerical results are presented to demonstrate that the proposed algorithm is superior to other resource allocation strategies in terms of energy efficiency.

Distributed space-time block codes (DSTBCs) have been developed to exploit diversity gains in cooperative communications systems. In this paper, we propose a new DSTBC based on unique word (UW) extension, referred to as the D-UW-STBC. The D-UW-STBC is devised for wireless relay networks with the amplify-and-forwarcl protocol and frequency selective fading channels. The data is transmitted from the source to the destination by a block-wise manner, resembling the block level of the Alamouti scheme. At the source, a UW is padded to the tail of each data block, which plays as a cyclic prefix, and thus allows for low-complexity implementation in the frequency domain. The additional purpose of using UW in this paper is to estimate the channels. However, the introduction of UWs makes it difficult to decouple the detection of data blocks. To achieve the orthogonality of the equivalent space-time channel, we carefully cancel the interference induced by the UWs. Also, a least square (LS) channel estimation approach is proposed, in which, the relay is transparent to the source and destination. The optimal UWs arc designed to minimise the effect of additive noise. Bit-crror-ratc (BER) performance comparison of various receiver schemes is carried out by computer simulations.

We develop a scheme to improve data throughput for multiuser cooperative relay communications operating in half-duplex mode. Cooperative relay, while effective in mitigating fading effects, might reduce the overall throughput of the network since it requires additionally resources for relay. In order to overcome this limitation, we develop a multiuser cooperative communication scheme that employs hierarchical modulation. This scheme exploits the different fading conditions for each user and allows the system to transmit two independent data streams simultaneously. Since the bit-error rate of the proposed system is a function of the distance parameters of hierarchical modulation, transmission reliability can be controlled flexibly by varying the distance parameter. We derive the error-rate expressions of the proposed scheme and compare its symbol-error rate performance for specific distance parameters with that of conventional relay schemes.

This paper proposes the distributed space-time block code (D-STBC) over frequency selective fading channel that achieves both spatial diversity gain and low decoding complexity with decoupling property in amplify-and-forward (AF) relay networks. These two goals are simultaneously achieved by our proposed code design, where the source permutates and conjugates the transmitted data before sending to the second relay. The diversity gain is investigated by analyzing the pairwise error probability (PEP) of the proposed scheme. In the analysis, we assume that one hop is line-of-sight (LOS) transmission modeled by Rician fading and the other hop is non-line-of-sight (NLOS) transmission experienced by Rayleigh fading. For each case, the PEP is derived based on the corresponding fading channel model.

This paper proposes a new distributed space-time block code (DSTBC) for single-carrier communications systems based on training sequence (TS). The proposed DSTBC is devised for amplify-and-forward (AF) relay networks over frequency selective fading channels. The data is transmitted from the source to the destination by a block-wise manner, resembling the block level of Alamouti scheme. A TS is padded to the tail of each information-bearing data block. The use of TS in this paper is twofold. First, it plays as a cyclic extension, thereby allowing us to construct a low-complexity receiver in the frequency domain. Second, it can be used for channel estimation. In contrast to zero padding technique, the introduction of TS makes it difficult to decouple the detection of data blocks. To recover the orthogonality of the equivalent space-time channel, we carefully treat the interference induced by the training sequences. As the second contribution, a least square (LS) channel estimation approach is also proposed for the proposed DSTBC. The optimal training sequences are designed to minimize the effect of additive noise. Bit-error-rate (BER) performance comparison is carried out by computer simulation.

We analyze diversity performance of scalar fixed- gain amplify-and-forward (AF) cooperation in multiple-input multiple-output (MIMO) relay channels with 𝓃ssource antennas, 𝓃Rrelay antennas, and 𝓃Ddestination antennas. We first derive the exact symbol error probability (SEP) for maximum likelihood decoding of orthogonal space-time block codes with M-ary phase-shift keying modulation over such channels and then characterize the effect of MIMO cooperative diversity on SEP behavior in a high signal-to-noise ratio regime. We show that the simple scalar-gain AF cooperation can create the diversity order dAF≤nSnD+nSnRnD/max{nS,nR,nD} with the equality if 2max{nS,nR,nD}≥nS+nR+nD-1. This finding reveals that the number of relay antennas greater than or equal to nS+ nD- 1 is required to achieve the additional diversity order nSnDby scalar-gain AF relaying. We also present the asymptotic SEP as the number of relay antennas tends to infinity.

This letter proposes a hybrid decision-feedback equalizer (HDFE) for DS-CDMA systems. The proposed HDFE is carried out in two stages to improve the accuracy of the feedback signals by exploiting the spreading gain in the feedback filter. The spread signals for a symbol are buffered and then detected, after which re-spreading is applied to generate feedback signals at the chip level. Through the use of symbol detection for feedback filtering, more accurate feedback signals are achieved. Simulation results demonstrate the superior error performance of the proposed scheme over the frequency domain linear equalization (FD-LE) and RAKE schemes in highly dispersive channels.

In this paper, we analyze the effect of the line-of-sight (LOS) on the symbol error probability (SEP) of nonregenerative cooperation in multiple-input multiple-output (MIMO) dual-hop relay channels with nSsource antennas, nRrelay antennas, and no destination antennas-referred to as a (nS,nR,nD)-MIMO dual-hop nonregenerative relay channel. In particular, we consider the channels of the source-to-relay (S-to-R) and the relay-to-destination (R-to-D) links are Rayleigh and Rician fading distribution, respectively. To be specific, we derive the exact SEP for maximum likelihood (ML) decoding of orthogonal space-time block codes (OSTBCs) over such channels and validate the analytical results by comparing with Monte-Carlo simulation. It is shown that for a fixed channel gain a strong LOS component degrades the error performance, e.g. SEP, of MIMO cooperative communications due to the lack of scattering.

This paper proposes a novel hybrid decision-feedback equalizer (HDFE) for direct sequence code-division multiple-access (DS-CDMA) systems to improve their performance in highly time-dispersive fading environments. In the proposed scheme, despreading and re-spreading are integrated in the feedback process to improve the accuracy of feedback signals. Instead of performing chip detection to obtain the instantaneous feedback signals as in the conventional HDFE, the authors buffer the spread signals for a symbol, carry out the despreading, and then apply symbol detection to derive the feedback signals. In the feedback process, re-spreading is applied since equalization must be implemented at 'chip-level'. Through the use of symbol detection and re-spreading, more accurate feedback signals are achieved. Additionally, the proposed method effectively mitigates the effect of error propagation that may dramatically degrade the performance of conventional decision-feedback equalization schemes. Simulation results demonstrate the superior error performances of the proposed scheme over the conventional HDFE and RAKE schemes in highly dispersive channels such as those described in the recommendation ITU-M.1225 for mobile communications.

As an important space-time code, V-BLAST (vertical-Bell lab layered space-time) code has been studied recently. Zero-forcing (ZF) and minimum mean square error (MMSE) are two nulling criteria that are commonly used in the V-BLAST system. In this paper, we propose the new detection algorithm for MMSE criterion that exterminates mutual interferences; hence the BER performance is improved. It can be done by modifying the channel matrix after each detection step. We also perform simulation to validate the analysis.

The effect of tap spacing on the performance of a RAKE receiver is analyzed analytically in a frequency-selective fading channel. A continuous time multipath fading channel model is used for the analysis, and the expression of the correlation between the desired signals, interference signals, and noise signals at the output of each branch of the RAKE receiver is derived for various chip waveforms. Since the noise components of each branch signal are correlated to each other, an optimum combining rule based on the maximum-likelihood criterion is derived to gain utmost performance. It is shown that the performance of the system can be improved by setting the tap spacing of the RARE receiver below the chip duration when the bandwidth of the transmitted signal is larger than the inverse of the chip duration. Also, it is shown that the normalized capacity of the system can be increased by using a chip waveform occupying wider bandwidth, which takes advantage of the increased diversity gain merits of a wide-band code-division multiple-access system at the same chip rate. It is noted that the derived combining rule gives diversity gain against the fading process as well as noise whitening processing gain against multiple-access interference at the same time.

In this letter, a timing control algorithm is described, which realizes timing synchronization on the direct sequence code-division multiple-access reverse link. In addition, the uncoded bit-error probability is analytically derived. Numerical results, confirmed by simulation, show that our synchronous transmission technique can offer better performance than conventional asynchronous transmission, especially for an exponentially decaying multipath intensity profile with a large decay factor.

The authors comment that the probability density function (PDF) of the signal-to-noise ratio (SNR) for third-order selection combining (SC3) given by Eng, Kong and Milstein (see ibid., vol.44, p.1117-29, 1996) is incorrect. A correction is given by presenting a more efficient method of deriving the generalized PDF of the SNR essential in the analysis of Nth-order selection combining.