While millimeter wave (mm-Wave) frequencies can meet the high data rate demands, their combination with high-mobility scenarios causes significant Doppler shifts that degrade the error performance of the commonly used orthogonal frequency division multiplexing (OFDM) modulation. Orthogonal time frequency space (OTFS) modulation has been introduced as an alternative approach that offers resilience to Doppler shifts by modulating symbols directly in the delay-Doppler (DD) domain. Although many studies have demonstrated that OTFS modulation outperforms OFDM in terms of error performance, these evaluations are largely influenced by the particular channel equalization method employed. In this paper, we focus on three linear minimum mean-square error (MMSE) channel equalization and detection in the time, frequency, and DD domains, and we investigate the error performance of OTFS and OFDM in high-mobility mm-Wave channels with various coding rates and modulation orders. The simulation results show that OTFS significantly outperforms OFDM in terms of error performance when the frequency domain equalization is applied to OFDM, regardless of the modulation order and coding rate. However, this advantage diminishes when time domain equalization is used with high-order modulations and low coding rates. In particular, OFDM shows a signal-to-noise ratio (SNR) of 0.8 dB better than OTFS in error performance when using 64-quadrature amplitude modulation (QAM) and a coding rate of 251/1024.

Reducing transceiver complexity and power consumption are important design factors of next-generation radio communication systems. In this paper, a dual-band single-chain radio system is demonstrated. The Digital Front-End (DFE) is based on the AMD RFSoC$\mathbf{4}\times \mathbf{2}$platform, and the Radio Frequency Front-End (RF-FE) is based on a connectorised architecture using commercial-off-the-shelf (COTS) products. Measured results characterise the error vector magnitude (EVM) and block error rate (BLER) of a dual-band, single-chain radio system across four modulation schemes, demonstrating comparable performance in both frequency bands. In addition, single-band measurements were conducted for comparison, revealing that the dual-band configuration maintains performance levels similar to those of the single-band setup. This highlights the advantages of the dual-band architecture, which supports multiple frequency bands without compromising performance. It significantly reduces transceiver complexity and power consumption, presenting a compelling alternative to implementing dual-band transceivers by duplicating radio chains.

Reducing transceiver complexity and power consumption are critical considerations in the design of next-generation radio communication systems. This work demonstrates a dual-band, single-chain radio unit for neutral host Open RAN applications. The radio unit features a Digital Front-End (DFE) implemented on the AMD RFSoC$4\mathrm{x}2$platform and a Radio Frequency Front-End (RF-FE) constructed using connectorised commercial-off-the-shelf (COTS) components. The error vector magnitude (EVM) and block error rate (BLER) performance of the dual-band radio system are measured under customisable test conditions, highlighting the radio's flexibility.

Reducing receiver complexity and power consumption are important design goals in fifth-generation (5G) millimeter-wave (mm-wave) communications systems. One approach for achieving these goals is to employ direct intermediate frequency (IF) sampling at sub-Nyquist rates in a superheterodyne receiver architecture using digital downconversion of the IF signal. This paper presents original measured results characterizing in detail the signal-to-noise-ratio (SNR), error vector magnitude (EVM), and block error rate (BLER) performances of a direct IF subsampling mm-wave receiver with subsampling rate as a parameter. A software-defined radio (SDR) receiver using direct IF subsampling was implemented in a 28GHz, beamforming, over-the-air (OTA), hardware-in-the-loop (HWIL), SDR testbed using a 2.52 GHz IF. For a quadrature phase shift keying (QPSK) modulated long-term evolution (LTE) signal subsampled at 500 MHz, a small SNR penalty of ≈3dB at 5% BLER was obtained over a 10 GHz Nyquist sampling benchmark.

Direct radio frequency (RF) sampling receivers are investigated for use in concurrent multiband reception for mobile broadband (MBB) applications. The recent proliferation of different frequency bands and standards in wireless communications has allowed large increases in mobility and throughput, but the number of receivers in a device is limited by physical space and power consumption. Software Defined Radio (SDR) is increasingly being explored to reduce the number of analog RF components required. This paper examines the use of direct RF digitization, allowing tunable and concurrent reception of multiple bands with a single RF front-end. Full mathematical models of both Nyquist and subband sampling receivers are presented and used to investigate a quadband LTE receiver, which is modeled in Simulink and implemented in a hardware-in-the-loop (HWIL) testbed. Individual bands are simulated to have at worst -95dBm sensitivity for 16-QAM with Nyquist sampling and -83dBm with subband sampling. Desensitization of the receivers due to multiband processing is evaluated theoretically and experimentally, showing a maximum of 3dB degradation, which is within the LTE standard for adjacent band interference.

As radio access networks (RANs) are becoming more densified, their design has shifted from considering capacity and coverage only to considering capacity, coverage and energy efficiency (EE). Also, sleep modes are an effective approach for enhancing the EE of densified RANs. This paper investigates the EE of a densified RAN for an Internet-of-Things (IoT) use case by employing a 3-dimensional (3D) Homogeneous Poisson Point Process (HPPP) to model the IoT base station (BS) distribution, which accounts for variation in BS height z as well as its x, y position. The EE performance of an IoT RAN is evaluated as the ratio of RAN throughput to RAN power consumption with the number of base stations varied as a parameter. The results demonstrate that sleep mode has the potential to make dense IoT networks energy efficient providing base stations serving only inactive or unconnected IoT devices are completely turned off, including the backhaul.

The base station (BS) densification in Internet of Things (IoT) networks provides a viable pathway for enhancing network capacity to meet the ever increasing demand for data. Increasing the number of BSs also increases the energy consumption, which compromises the network energy efficiency (EE). This is important in 3 dimensional (3D) IoT deployments where volume spectral efficiency (VSE) and EE are key performance indicators (KPIs). In such networks, BS sleep modes provide an effective way to constrain both the interference and energy consumption, thereby improving the EE. In this paper, both the VSE and EE of a densified 3DIoT network are investigated when BS and UE counts follow independent 3D Homogeneous Poisson Point Process (HPPP) models and UEs are placed either uniformly or in clusters. The simulation results show that when unloaded BSs are turned off completely, including the backhaul, sufficiently densified 3DIoT networks can be made energy efficient.

Abstract Direct RF sampling has been suggested as a solution for receivers that are flexible in frequency and across standards, while utilising only a single radio frequency front‐end. However there are concerns about their robustness in the presence of out‐of‐band and in‐band blockers. Tunable filtennas offer a solution to this, incorporating filtering into the antenna space while providing rejection of unwanted signals. This paper presents a filtenna containing reconfigurable frequency selective surfaces to provide tunable filtering between 1.44 and 1.95 GHz. The filtenna is characterised as an antenna and a filter, showing minimum 18 dB rejection across the principle beamwidths. It is then implemented in a direct RF sampling receiver and is shown to provide sufficient rejection of blockers to cause no degradation in the received error vector magnitude (EVM) and block error rate (BLER) of LTE signals when subject to 5G NR‐compliant blocking signals. The in‐band blocker performance is also characterised, showing at most 3 dB degradation in EVM and BLER.

Connectivity using interband frequencies in 4G and 5G radio access networks, for example, carrier aggregation or dual-connectivity, incurs high receiver complexity and power consumption, in particular, when implemented using multiple radio units. Employing concurrent, multiband, direct RF sampling in a single radio chain architecture reduces the RF component count, leading to lower receiver complexity and power consumption. For this architecture, as the composite signal from multiple concurrent bands is digitized by a common analog-to-digital converter (ADC), the bit resolution critically affects system performance. In this paper, the effect of ADC resolution on the error vector magnitude (EVM) and Block Error Rate (BLER) performance of a concurrent, multiband, direct RF sampling receiver is investigated. Simulation and hardware measurement of a tri-band Long Term Evolution (LTE) system supporting three simultaneously active channels at 888 MHz, 1.92 GHz and 2.52 GHz is evaluated when reducing the ADC resolution from 8 to 3 bits. Interband interference measurements demonstrate that the multiband, direct RF sampling, wideband LTE receiver remains 3GPP compliant at 4-bit ADC resolution with the signal-to-noise-ratio (SNR) desensitization over a single-band receiver limited to 9 dB in the 888 MHz band.

Energy-constrained slot-amplitude modulation (ECSAM) enables light dimming, eliminates light flicker and constrains the peak optical power while providing robust communication links. However, the complexity of the maximum-likelihood (ML) based ECSAM receiver increases exponentially with required spectral efficiency. This paper provides a comprehensive performance evaluation of ECSAM for the indoor visible light communication (VLC) channel with multipath propagation under realistic illumination constraints and imperfect channel estimation. A sub-optimal receiver that employs a slot-by-slot detection algorithm followed by a slot-correction mechanism for reducing the receiver complexity is proposed. Additionally, the method for optimal selection of parameters when designing the signal waveform is presented. The analytical upper bound on the symbol error rate of ECSAM is derived using the union-bound technique. The results show that the error performance of the sub-optimal receiver are comparable to that of the optimal ML receiver. Compared with conventional power or bandwidth efficient VLC modulation techniques such as multiple pulse position modulation (MPPM) and pulse amplitude modulation (PAM), ECSAM provides complete flexibility in modifying the signal constellation for a desired dimming level to maximise the spectral efficiency and provide a robust bit error rate performance especially in the multipath propagation channel induced intersymbol interference.

A Direct Antenna Modulation (DAM) transmitter is modelled in wideband channels using Direct Sequence Spread Spectrum (DSSS) as a low-cost, low-complexity solution for the Internet of Things (IoT). Metasurface-based DAM is an emerging technique where a baseband signal is modulated directly onto a radio frequency (RF) carrier wave using a reconfigurable metasurface. This technique removes the requirement of the power amplifier (PA) to amplify complex modulated signals, allowing the use of a simple, energy efficient PA to amplify only the carrier wave. The reduction in power consumption and RF electronics makes DAM an attractive low-cost, low-complexity transmitter technology. This paper discusses the use of a DAM transmitter as an IoT access point transmitter using DSSS to overcome broad-band fading and mitigate the systematic distortion inherent in the technique. Simulation shows DAM to have negligible impairment in 3GPP urban channels compared with ideal modulation when balanced spreading codes are used.

A concurrent, tunable, tri-band, single chain radio receiver for 5G radio access networks is evaluated. The three concurrent bands are independently tunable over a frequency range from 600 MHz to 2.7 GHz. A hardware-in-the-loop test-bed provides a system level evaluation of the proposed receiver using direct RF digitization. The test-bed emulates a 5G heterogeneous network supporting three wideband, simultaneous connections. By measuring the receiver EVM, we demonstrate sufficient isolation between concurrent bands achieving 60 MHz of aggregated bandwidth as well as strong resilience to adjacent blockers.

A concurrent, tunable, triple-band, single chain radio receiver for 5G radio access networks is presented and its performance is evaluated in a hardware-in-the-loop test-bed. The test-bed emulates a 5G heterogeneous network supporting three independently tunable, wideband, simultaneous connections over a frequency range from 600 MHz to 2.7 GHz. The single chain receiver is able to achieve an aggregate bandwidth of 93.75 MHz, 31.25 MHz per band, and a net data rate of 187.5 Mbit/s through the use of single-carrier QPSK transmissions. The receiver demonstrate sufficient isolation between the concurrent transmissions as well as strong resilience to adjacent blockers through the use of a small guard band.

This invited paper considers a key next step in the design of radio architectures aimed at supporting low energy consumption in 5G heterogeneous radio access networks. State-of-the-art mobile radios usually require one RF transceiver per standard, each working separately at any given time. Software defined radios, while spanning a wide range of standards and frequency bands, also work separately at any specific time. In 5G radio access networks, where continuous, multiband connectivity is envisaged, this conventional radio architecture results in high network power consumption. In this paper, we propose the novel concept of a concurrent multiband frequency-agile radio (CM-FARAD) architecture, which simultaneously supports multiple standards and frequency bands using a single, tunable transceiver. We discuss the subsystem radio design approaches for enabling the CM-FARAD architecture, including antennas, power amplifiers, low noise amplifiers and analogue to digital converters. A working prototype of a dual-band CM-FARAD test-bed is also presented together with measured salient performance characteristics.

In order to meet the high data rate, low latency and high energy efficiency requirements, the future radio units must utilise the frequency spectrum available at certain geographical location efficiently with a minimum amount of hardware. This requires frequency agility and concurrent multi-standard operation capabilities at the base and mobile terminals. To utilise the TV white spaces for mobile and wireless communication and enable their carrier aggregation with sub GHz LTE bands, this paper presents a single-chain, reconfigurable, RF digitising, dual- band receiver comprised of a tunable dual-band antenna, a reconfigurable digital down converter, a baseband processing unit and wideband LNA and ADC in the form of an oscilloscope. The presented dual-band receiver is tested through a hardware- in-the-loop test-bed which shows that up to 20 MHz aggregate bandwidths can be achieved. The receiver is able to provide equivalent error vector magnitude (EVM) performance across a wide range of frequencies avoiding any inter-band interference.

A Novel method to evaluate the energy efficiency of different MIMO schemes is proposed in this paper, where the LTE radio base station power consumption is estimated by using an accurate power consumption model. The energy consumption gain (ECG) is used as a metric, and it is calculated for a MIMO base station with reference to a SISO base station. The results show that the MIMO base station cannot be more energy efficient than the SISO base station if the MIMO overhead power increases by more than 20%. The energy efficiency of MIMO base station can be improved by adapting the number of active transmit antennas according to the offered traffic load intensity. Moreover, the energy efficiency of an LTE RAN is evaluated when the network has been dimensioned by assuming MIMO base stations. The obtained results show that when spatial multiplexing schemes are assumed, and under the same requirements of coverage and traffic load, the MIMO RAN can be more energy efficient than the SISO RAN, even if the MIMO base station overhead power is increased by 60%.

Analysing the performance of WLANs in non-ideal channel conditions is a fundamental consideration in practical situations since wireless channels are error-prone. This paper presents a closed form analytical solution for the non-saturated throughput of a QoS differentiated p-persistent CSMA protocol that takes into account the capture effect in a Rayleigh multipath fading environment. The results show that the throughput performance with the capture effect depends on the absolute and relative p-persistent values, the total system offered load and relative offered loads per traffic type, as well as the thresholds for capture.

Colour shift keying (CSK) is a visible light communication (VLC) modulation scheme, designed for multi-colour light emitting diodes (LEDs), standardised in IEEE 802.15.7. The standard specifies a Reed-Solomon (RS) encoder for the CSK physical layer (PHY). Currently, no investigations have been made to analyse the performance of the RS coded CSK. This paper details, that the CSK systems yield to soft de-mapping, allowing the soft-decision binary convolutional (SD-BC) coding to be used, and evaluates the performance of RS, SD-BC and hard-decision binary convolutional (HD-BC) coded CSK systems. The throughputs of the three colour (TLED) and four colour (QLED) based, coded and uncoded, CSK systems are compared over the additive white Gaussian noise (AWGN) and wireless VLC channels, with colour crosstalk and insertion losses (CIL). A throughput vs operating-range analysis is also presented. The results show that the SD-BC scheme proves to be the most efficient of the coded systems investigated and that the HD-BC coded CSK systems will outperform the RS coded CSK as the SNR increases. The SD-BC coded TLED and QLED systems, when compared to RS coded equivalents, provide up to 2 and 6 dB optical SNR gain over AWGN channel, and up to 2.3 and 5.7 dB optical SNR gain over the indoor VLC channel, respectively. The performance of the uncoded CSK systems has also been approximated analytically for the AWGN channel.

Spatial complementary code keying modulation (SCCKM) is proposed as a novel block coding modulation scheme. An input binary sequence is modulated based on the different lengths of complementary code keying (CCK) modulation and then spread across the transmit antennas (spatial domain) in a multiple input multiple output (MIMO) system exploiting orthogonal frequency division multiplexing (OFDM). At the receiver side, zero forcing equalization is applied to the OFDM modulated data to mitigate the effect of the multipath fast fading channel and then followed by maximum likelihood (ML) detection to retrieve the input sequence. The performance of SCCKM in different MIMO systems is compared to that of spatial modulation (SM) as a baseline scheme. Simulation results show that for the same spectral efficiency, SCCKM is able to substantially improve the bit error rate (BER).

This work presents the higher order modulation schemes for the standardised trichromatic light-emitting diode (TLED) and recently developed quad-chromatic LED (QLED) based colour shift keying (CSK), and investigates their performance over diffuse optical wireless channels with colour cross-talk, insertion losses and additive white Gaussian noise (AWGN). The performance analysis shows that the uncoded and unequalised QLED CSK can provide up to 288 Mbit/s data links, using standard compliant optical clock rate, through the use of a 4096 level modulation scheme, which is the highest number of levels so far been developed for a CSK scheme. Additionally, the results show that QLED scheme has better spectral and power efficiencies than the TLED scheme as the 256-CSK of QLED requires 4.5 dB less optical power than the 64-CSK of TLED when the normalised delay spread is increased to 0.25. The performance of both the CSK schemes is also examined without the use of colour calibration, which reveals that 4-CSK of QLED scheme can operate without the receiver having any knowledge of the colour cross- talk, which makes this modulation format an ideal signalling channel for the estimation of colour cross-talk and impulse response of optical channel. The analytical approximations, for the bit error performance of all the modulation orders, with AWGN are also presented.

Green wireless communications have received increasing attention from government, academia, and industry. However, how to define a green wireless communication system has been an open topic. In this paper, firstly, we present the definition of green efficiency of wireless links and carry out a comprehensive analysis of the efficiency metrics, e.g., the b/s/Hz spectrum efficiency, the b/s/Hz/W energy efficiency, the b/TENU power efficiency and our proposed (b·m)/s/Hz/W green efficiency of a wireless link, in particular we can prove that green efficiency is a strict convex function with respect to transmission power and distance. Secondly, by tuning the cell size with users' QoS (quality of service) guarantee, we introduce green efficiency into a cellular network and achieve the theoretical upper bound of green efficiency for a cellular network. Finally, we present a green efficiency-based network planning method for practical environment. Simulation results show that the proposed network planning mechanism can approach the upper bound of green efficiency.

This paper presents the results of a joint investigation conducted between academia and industry. The investigation focused on modelling and reducing the energy expenditure of a 4G LTE network in a London case-study area, using data sets from an existing 3G network deployment. In the first part of the paper, different multi-cell network modelling approaches were compared, including: stochastic and linear geometry, hexagonal cell layout with wrap- around, and realistic network topology. The impact of terrain and clutter is also examined. It was found that they had a similar performance profile (80%) correlation, and a back-off factor to translate theoretical to measured results can account for most of the differences. The second part of the paper focuses on effective techniques that can be used to reduce energy consumption. Sleep mode and heterogeneous networks are combined and an ERG of 15-46% is achieved.

In cellular networks, balancing the throughput among users is important to achieve a uniform Quality-of-Service (QoS). This can be accomplished using a variety of cross-layer techniques. In this paper, the authors investigate how the down-tilt of base-station (BS) antennas can be adjusted to maximize the user throughput fairness in a heterogeneous network, considering the impact of both a dynamic user distribution and capacity saturation of different transmission techniques. Finding the optimal down-tilt in a multi-cell interference-limited network is a complex problem, where stochastic channel effects and irregular antenna patterns has yielded no explicit solutions and is computationally expensive. The investigation first demonstrates that a fixed tilt strategy yields good performances for homogeneous networks, but the introduction of HetNet elements adds a high level of sensitivity to the tilt dependent performance. This means that a HetNet must have network-wide knowledge of where BSs, access-points and users are. The paper also demonstrates that transmission techniques that can achieve a higher level of capacity saturation increases the optimal down-tilt angle. A distributed reinforcement learning algorithm is proposed, where BSs do not need knowledge of location data. The algorithm can achieve convergence to a near-optimal solution rapidly (6-15 iterations) and improve the throughput fairness by 45-56% and the energy efficiency by 21-47%, as compared to fixed strategies. Furthermore, the paper shows that a tradeoff between the optimal solution convergence rate and asymptotic performance exists for the self-learning algorithm.

In this study, the impact of a Radio‐over‐Fibre (RoF) subsystem on the capacity performance of wideband code division multiple access is evaluated. This study investigates the use of pilot‐aided channel estimation to compensate for the optical subsystem non‐linearities for different channel conditions, estimation intervals and coding schemes. The results show that pilot‐aided channel estimation is an effective method for compensating the composite impairments of the optical subsystem and the radio frequency (RF) channel. It is found that there is always a suitable pilot power level which maximises the system capacity performance regardless of coding scheme and channel condition. Also, the peak capacity is only slightly affected by a decrease in the estimation interval.

This paper addresses the challenge of how to reduce the energy consumption of a multi-cell network under a dynamic traffic load. The body of investigation first shows that the energy reduction upper-bound for transmission improving techniques is hardware-limited, and the bound for infrastructure reduction is capacity-limited. The paper proposes a novel cell expansion technique, where the coverage area of cells can expand and contract based on the traffic load. This is accomplished by switching off low load cell-sites and compensating for the coverage loss by expanding the neighboring cells through antenna beam tilting. The multi-cell coordination is resolved by using either a centralized controller or a distributed self-organizing-network (SON) algorithm. The analysis demonstrates that the proposed distributed algorithm is able to exploit flexibility and performance uncertainty through reinforced learning and improves on the centralized solution. The combined energy saving benefit of the proposed techniques is up to 50% compared to a reference deployment and 44% compared with alternative state-of-the-art dynamic base-station techniques.

This paper presents closed-form capacity expressions for interfere-limited relay channels. Existing theoretical analysis has primarily focused on Gaussian relay channels, and the analysis of interference-limited relay deployment has been confined to simulation based approaches. The novel contribution of this paper is to consolidate on these approaches by proposing a theoretical analysis that includes the effects of interference and capacity saturation of realistic transmission schemes. The performance and optimization results are reinforced by matching simulation results. The benefit of this approach is that given a small set of network parameters, the researcher can use the closed-form expressions to determine the capacity of the network, as well as the deployment parameters that maximize capacity without committing to protracted system simulation studies. The deployment parameters considered in this paper include the optimal location and number of relays, and resource sharing between relay and base-stations. The paper shows that the optimal deployment parameters are pre-dominantly a function of the saturation capacity, pathloss exponent and transmit powers. Furthermore, to demonstrate the wider applicability of the theoretical framework, the analysis is extended to a multi-room indoor building. The capacity improvements demonstrated in this paper show that deployment optimization can improve capacity by up to 60% for outdoor and 38% for indoor users. The proposed closed-form expressions on interference-limited relay capacity are useful as a framework to examine how key propagation and network parameters affect relay performance and can yield insight into future research directions.

In this paper, a comprehensive and new closed form analytical approach to calculate the saturated throughput and delay of a differentiated p-persistent CSMA protocol with a multirate capability is presented for the first time. The p-persistent analysis can be used to model accurately 802.11e EDCA for WLAN applications. The analysis allows 802.11e to be characterised in the case of multirate operation without undue numerical complexity unlike state-of-the-art analytical approaches.

Wireless communications has been recognized as a key enabler to the growth of the future economy. There is an unprecedented growth in data volume and the associated energy consumption. The challenge addressed in this paper is how to meet the growth in data traffic, whilst reducing both the cost and energy consumed. The paper shows that small cell deployments can significantly reduce energy consumption (30%), but increase the network cost (14%). The novel characterization of the tradeoff between Capacity, Energy and Cost (CEC) is of importance to researchers and operators.

This paper analyzes the fundamental tradeoff between the total power consumption and the downlink capacity in an interference limited LTE network. In order to achieve significant energy savings, a re-deployment of the cell-sites is needed. The paper employs a novel power consumption and capacity tradeoff to assist the process of re-deployment and show that up to 75% energy can be saved. The implication of this paper's results has a significant impact both on commercial revenue and the environment by reducing up to 24 power plants world wide.

This paper addresses the challenge of designing a cellular network that can meet a dynamic range of offered traffic loads at a low energy level. Cellular networks are conventionally deployed to meet a high traffic load and can be energy inefficient at lower loads. The paper proposes a novel cell expansion technique that can reduce total energy consumption by up to 46% depending on the offered load. Dynamic cell expansion switches off a certain pattern of cell-sites in accordance with traffic load and allows neighbouring cells to compensate by expanding their coverage. A key novelty is achieving this via creating inner and outer cell regions using vertical sectorization and adaptively tilting outer cell antennas to expand and contract cell coverage. Furthermore, a management service is proposed to handle contention between competing cells. The gains achieved compared to existing techniques is 22% higher and the results of this paper can have a profound impact both on the operators' revenue and global environment, reducing up to 11 power plants world wide.

Inter-cell interference (ICI) is a key limiting factor to the general performance of a multi-cell multi-user radio access network. The channel quality of cell edge users is greatly impaired by ICI owing to the fact that cell edge users are furthest away from the their serving base station and closest to the interfering base stations. As a result the Quality of Service (QoS) and energy efficiency of the E-UTRAN is primarily dependant on the cell edge users. Firstly, we propose a new Time Domain Packet Scheduling criterion that endeavours to reduce the variation in the energy performance, of the users, in a temporal sense. The proposed criteria aims to strike a balance between two user prioritisation criteria that result in energy performance at the two extremes of the energy consumption range. The paper shows that this improves the mean energy efficiency of the E-UTRAN. Secondly, we introduce an energy optimisation algorithm to complement the Time Domain Packet Scheduler. The new energy aware packet scheduling criteria is compared against the established throughput based proportional fair scheduler with uniform power allocation and is shown to produce 20% Energy Reduction Gains (ERG) without compromising the spectral efficiency and QoS performance.

The objective of this paper is to provide the methodology and results that is used to evaluate a scalable energy performance comparison of LTE-femtocells and 802.11n with both SISO and MIMO antenna configurations. The performance is derived in a multi-user and multi-cell wireless communication system. A system level LTE-femtocell simulator has been developed and an analytical model to evaluate 802.11n network performances has been proposed. It is shown that 1 Femtocell Access Point consistently perform better than 1 802.11n Access Point. This may be explained by the centralised resource allocation and channel access methods used by femtocells compared to distributed methods and CSMA/CA used by 802.11 networks. Generally, SISO deployment is more energy efficient than Alamouti MIMO 2×2.

The purpose of this paper is to show that the indoor downlink capacity and energy efficiency can be significantly improved by optimising the indoor location of femtocell. This body of investigation is done in the presence of outdoor interference and the simulation results are backed up by a novel theoretical framework employing convex optimisation. Moreover, this optimisation problem has been demonstrated to be meaningful in the context of considering capacity saturation of realistic modulation and coding schemes. The results yield insight into the relationship between the outdoor and indoor aspects of the cellular network, as well as the propagation parameters. The paper shows that a mean capacity improvement of up to 20% can be made with optimal placement, which translates to an operational energy reduction of 8%. Moreover, it has been shown that the optimisation does not significantly degrade the performance of outdoor network. The global impact of this work is that 1.6 TWh can be saved globally, which amounts to the energy produced by two 1000 MW power plants.

The trade-off between energy efficiency and downlink spectral efficiency for LTE-femtocells can be significantly balanced by a novel interference management technique in the presence of the interference from the co-channel outdoor micro-cell and the neighbouring femtocell access points. The simulation results have been demonstrated to be meaningful in the context of considering capacity saturation of realistic modulation and coding schemes rather than theoretical Shannon's equation. The paper shows that the radio-head and operational improvement of up to 12% and 3% can be achieved. Moreover, it has been shown that the improvement does not significantly degrade the user's data rate and the proposed scheme can be implemented in unplanned self- organising networks.

The IEEE 802.11e standard allows for contention-based quality of service (QoS) provisioning using enhanced distributed channel access (EDCA). By tuning the contention parameters for EDCA, the system can adapt to changes in the network scenario. The benefits of this adaptation include the ability to maximise the system capacity while also achieving the service differentiation necessary to provide QoS. The use of fixed sized contention windows is one simple and effective way to improve EDCA performance and this can be modelled as p-persistent carrier-sense multiple access (CSMA). In this study a straightforward throughput and delay analysis is provided for p-persistent CSMA that can be easily applied to an EDCA system within the rules of the current 802.11 standard. Several versions of the analysis are provided to show how further parameters of EDCA can also be included and their effects on system performance are shown. These further parameters include transmission opportunities, internal collision resolution, AIFS differentiation and retry limits. Any number and combination of these further parameters can be included at the same time making this new form of analysis extremely flexible as well as accurate to model a wide variety of EDCA system scenarios.

Inter-cell interference (ICI) is a key limiting factor to the radio frequency (RF) energy performance of a multi-cell multi-user radio access network (RAN). The channel quality of the cell edge users is greatly impaired by ICI owing to the fact that cell edge users are furthest away from their serving base stations (BSs) and closest to the interfering BSs. Consequently the BS is compelled to allocate more physical resource blocks [PRBs (In LTE a PRB spans 12 sub-carriers each with a bandwidth of 15 kHz over a 0.5 ms time slot)] to the cell edge users in order to meet their quality-of-service (QoS) targets. The study proposes a novel ICI management technique that mitigates the effects of ICI through a sequential game play between cells in the E-UTRAN [Evolved Universal Mobile Telecommunications Systems (UMTS) terrestrial radio access network] based on the instantaneous cell offered load. The proposed technique is shown to produce greater user channel quality improvements of 4 dB greater than the state-of-the-art ICI management techniques. The channel quality improvements result in a utilisation of less PRBs, RF and radio head energy which translate to energy reduction gains of 34 and 45% at low- and high-offered loads, respectively. In addition the proposed scheme does not require a central processing entity such as a radio network controller and can be implemented in unplanned self-organising networks.

With the rapid development of 802.11 wireless local area networks (WLANs) and the need for better quality of service (QoS) the 802.11e MAC with service differentiation was developed. Analysing the effect of transmission errors on the performance of 802.11 is a fundamental consideration in practical situations since the wireless channels are error-prone. This paper modifies the p-persistent CSMA protocol with multiple traffic types into a more accurate and practical model that takes into account the transmission errors when different traffic types experience different packet error rates. A new adaptive p-persistent protocol is presented that can reduce the effect of the transmission errors on the system throughput performance. The results show that transmission errors degrade the throughput performance by up to 62%. The adaptive p-persistent CSMA protocol alleviates the effect of this channel impairment and improves the throughput performance by 20%.

With the extensive deployment of 802.11 wireless local area networks (WLANs) and the need for better quality of service (QoS), the 802.11e MAC with service differentiation was developed. Analysing the effect of fading, shadowing and near-far effect on the performance of 802.11 is a fundamental consideration in practical situations since the wireless channels are error-prone. This paper develops a p-persistent CSMA protocol, which allows for service differentiation by using multiple traffic types, into an accurate and practical model that takes into account the capture effect in a Rayleigh multipath fading environment. A new analytical approach is developed to calculate the throughput and packet delay for multiple traffic types. Results provided for this new model show that the capture effect increases the throughput by 32% in a highly loaded system thereby demonstrating the importance of including the capture effect in wireless protocols.

In this paper, the implementation aspects and constraints of the simplest network coding (NC) schemes for a two-way relay channel (TWRC) composed of a user equipment (mobile terminal), an LTE relay station (RS) and an LTE base station (eNB) are considered in order to assess the usefulness of the NC in more realistic scenarios. The information exchange rate gain (IERG), the energy reduction gain (ERG) and the resource utilization gain (RUG) of the NC schemes with and without subcarrier division duplexing (SDD) are obtained by computer simulations. The usefulness of the NC schemes are evaluated for varying traffic load levels, the geographical distances between the nodes, the RS transmit powers, and the maximum numbers of retransmissions. Simulation results show that the NC schemes with and without SDD, have the throughput gains $0.5\%$ and $25\%$, the ERGs $7-12\%$ and $16-25\%$, and the RUGs $0.5-3.2\%$, respectively. It is found that the NC can provide performance gains also for the users at the cell edge. Furthermore, the ERGs of the NC increase with the transmit power of the relay while the ERGs of the NC remain the same even when the maximum number of retransmissions is reduced.

It is desirable that energy performance improvement is not realized at the expense of other network performance parameters. This paper investigates the trade off between energy efficiency, spectral efficiency and user QoS performance for a multi-cell multi-user radio access network. Specifically, the energy consumption ratio (ECR) and the spectral efficiency of several common frequency domain packet schedulers in a cellular E- UTRAN downlink are compared for both the SISO transmission mode and the 2×2 Alamouti Space Frequency Block Code (SFBC) MIMO transmission mode. It is well known that the 2×2 SFBC MIMO transmission mode is more spectrally efficient compared to the SISO transmission mode, however, the relationship between energy efficiency and spectral efficiency is undecided. It is shown that, for the E-UTRAN downlink with fixed transmission power, spectral efficiency improvement results into energy efficiency improvement. The effect of SFBC MIMO versus SISO on the user QoS performance is also studied.

Abstract Dedicated short range communications (DSRC) has been regarded as one of the most promising technologies to provide robust communications for large scale vehicle networks. It is designed to support both road safety and commercial applications. Road safety applications will require reliable and timely wireless communications. However, as the medium access control (MAC) layer of DSRC is based on the IEEE 802.11 distributed coordination function (DCF), it is well known that the random channel access based MAC cannot provide guaranteed quality of services (QoS). It is very important to understand the quantitative performance of DSRC, in order to make better decisions on its adoption, control, adaptation, and improvement. In this paper, we propose an analytic model to evaluate the DSRC‐based inter‐vehicle communication. We investigate the impacts of the channel access parameters associated with the different services including arbitration inter‐frame space (AIFS) and contention window (CW). Based on the proposed model, we analyze the successful message delivery ratio and channel service delay for broadcast messages. The proposed analytical model can provide a convenient tool to evaluate the inter‐vehicle safety applications and analyze the suitability of DSRC for road safety applications. Copyright © 2009 John Wiley & Sons, Ltd.

The objective of this paper is to combine the antenna downtilt selection with the cell size selection in order to reduce the overall radio frequency (RF) transmission power in the homogeneous High-Speed Packet Downlink (HSDPA) cellular radio access network (RAN). The analysis is based on the concept of small cells deployment. The energy consumption ratio (ECR) and the energy reduction gain (ERG) of the cellular RAN are calculated for different antenna tilts when the cell size is being reduced for a given user density and service area. The results have shown that a suitable antenna tilt and the RF power setting can achieve an overall energy reduction of up to 82.56%. Equally, our results demonstrate that a small cell deployment can considerably reduce the overall energy consumption of a cellular network.

CSMA/CA is a common access mechanism for contention based wireless channels. One of the ways in which quality of service in contention based wireless networks is achieved is by service differentiation. This can be realised by prioritising packets based on their importance while taking into account the network load. p-persistent CSMA is a form of CSMA/CA and in this paper an analytical model for the throughput and delay of a p-persistent CSMA system is developed where the system contains a finite number of non-saturated stations with both heterogeneous loads and priorities. Results based on this new model show how the throughput and delay for the traffic flows on the network are affected by the relative p-persistence and offered load values for all of the stations in the network.

Many home networks now use 802.11 wireless local area networks (WLAN)s. The 802.11e amendment has been designed to improve quality of service (QoS) over these networks allowing for multimedia applications such as IPTV to be better supported. The H.264 video compression standard is suitable for IPTV due to its high compression and error resilience. Video packets of different slice types are of varying importance to the decoded video quality so can be mapped into different priority queues using 802.11e enhanced distributed channel access (EDCA). We investigate several mapping schemes for a variety of video content to see how the quality of the decoded video is affected as the number of concurrent video connections is increased. The different mapping schemes exhibit different loss patterns in the video sequences and their impact on the video quality is content dependent. Subjective tests were therefore carried out which allow us to perform an accurate and valid assessment of the video quality. Packet loss rate is also reported. Our results show that as the number of concurrent videos approaches the network capacity some mapping schemes show a cliff-edge drop in quality while others offer a more acceptable gradual quality degradation. These schemes cause B-frames to be dropped and in effect reduce the video frame rate. These schemes are more successful for videos that have low or medium temporal activity.

This paper presents a novel WLAN-based system configuration employing Coded Multi-Carrier Code-Division- Multiplexing technology (CMC-CDM), as a potentially superior alternative to the currently standardized Coded OFDM (COFDM) technology. To further improve the performance of the system and reduce its complexity, a new concept of Chase detection is applied at the receiver. A comprehensive investigation has shown that under the appropriate conditions, the proposed system is able to show considerable advantage over COFDM. We believe that this work will contribute to the motivation of deploying CMC-CDM as an alternative approach for Next Generation of wireless systems.

In this paper we look at several techniques that can allow for the quality of downloaded video streams to be maintained when an 802.11e MAC becomes congested. These techniques come from two distinct groups: Packet mapping schemes and packet dropping schemes. The packet mapping schemes determine which 802.11e enhanced distributed channel access (EDCA) queue each video packet joins. One mapping scheme treats all packets equally, while the other differentiates the video packets of different slice types. The packet dropping schemes aim to avoid MAC layer congestion by dropping some of the packets before arriving at the MAC. Two packet dropping schemes are used which both differentiate video packets by trying to drop the lower importance packets first. One packet dropping scheme applies an even amount of loss to each video stream while the other applies an even statistic which results in an uneven amount of loss to each video stream. Results show that all of the schemes that differentiate video packets allow for a more gradual video quality degradation than would otherwise occur. The packet dropping schemes also provide the best delay performance. Results for each scheme are content dependant and the packet dropping scheme that results in uneven amounts of packet losses is the only scheme which treats all types of content well. We show that at high loads this scheme can offer a system performance with a mean opinion score that is at least 0.5 greater than any of the other schemes can provide.

In this paper new architectural approaches that improve the energy efficiency of a cellular radio access network (RAN) are investigated. The aim of the paper is to characterize both the energy consumption ratio (ECR) and the energy consumption gain (ECG) of a cellular RAN when the cell size is reduced for a given user density and service area. The paper affirms that reducing the cell size reduces the cell ECR as desired while increasing the capacity density but the overall RAN energy consumption remains unchanged. In order to trade the increase in capacity density with RAN energy consumption, without degrading the cell capacity provision, a sleep mode is introduced. In sleep mode, cells without active users are powered-off, thereby saving energy. By combining a sleep mode with a small-cell deployment architecture, the paper shows that the ECG can be increased by the factor n = (Rlarge/Rsmall)2while the cell ECR continues to decrease with decreasing cell size.

802.11 wireless local area networks are now common in the home. The 802.11e amendment allows for quality of service (QoS) provisioning over these networks to help meet the QoS demands of the growing number of multimedia applications on these home networks. The H.264 video coding standard is suitable for most multimedia applications due to its high compression and error resilience. This paper investigates how the quality of H.264 video is affected as the number of concurrent video streams sent over an 802.11e network is increased. We compare two traffic mapping schemes with and without the use of the flexible macroblock ordering (FMO) tool of H.264. We show that the mapping scheme which prioritises video packets based on their frame type is more successful at maintaining the quality of video when congestion occurs. A more gradual degradation in quality can be achieved rather than the cliff-edge drop that otherwise occurs. We also identify that errors caused by congestion tend to occur towards the bottom of each frame and that FMO can reduce this effect.

With the widespread success of 802.11 wireless local area networks (WLANs) and the need for quality of service (QoS) the 802.11e amendment was created. This amendment specifies the enhanced distributed channel access (EDCA) procedure which provides QoS through service differentiation. The underlying mechanism for the contention based access of 802.11 and 802.11e is carrier sense multiple access with collision avoidance (CSMA/CA). p-persistent carrier sense multiple access (p-persistent CSMA) can be used to model CSMA/CA. This paper modifies the p-persistent CSMA mechanism to provide service differentiation in a saturated network. This is a new general model for providing QoS through contention based access. This p-persistent CSMA model is then converted into a model for an 802.11e network. Simulations and comparison with other 802.11e models validates this model while the benefit of this model is that it can be modified readily to characterise service differentiation in a non-saturated network.

This paper studies the performance of a new coded multi-carrier code-division multiplexing (CMC-CDM) scheme in a wireless LAN (WLAN) context, employing different interleaving approaches. It is found that for high data rate transmission the proposed system has the potential to achieve power efficient PER performance using low complexity receivers. For example, equal gain combining (EGC) may be used effectively with an appropriate choice of bit, symbol or chip interleaving. The results show that EGC can be advantageously deployed without chip interleaving, where considerable performance improvement is realized. For delay-sensitive applications, where interleaving is not affordable, the proposed system can provide more than 5 dB improved power efficiency compared to the IEEE.11a standardized system.

The performance of a high data rate optical wireless system (OWS) over the diffuse indoor infrared channel based on direct sequence spread spectrum (DSSS) techniques is highly sensitive to the properties of the aperiodic autocorrelation function and the spreading factor of the spreading sequence used. Ideally, the aperiodic autocorrelation function should have zero sidelobes in order to eliminate intersymbol interference caused by multipath propagation. In practice, such an ideal sequence does not exist in the binary field when data modulation is applied. For high data rates, a small spreading factor is desired in order to avoid an excessive system bandwidth. The family of Barker sequences is investigated in a DSSS–OWS. The Barker sequences are binary spreading sequences which exhibit small aperiodic autocorrelation values and short spreading factors. The system bit error rate (BER) performance is characterized on the diffuse indoor infrared channel when using RAKE reception. Results of BER against Eb/No are presented with data rate and spreading factor as parameters. The results demonstrate that of the seven Barker sequences existing, the length three Barker sequence {0 0 1} provides the best system design trade-off in respect of good BER performance and low implementation complexity.

In this paper, we investigate the application of a unipolar non-coherent M-ary orthogonal keying (NC-MOK) for OFDM system that does not require channel estimation and compare its performance with that of bipolar Coherent MOK where for the latter phase information is obtained via pilot-based channel estimation. The performance of the orthogonal M-ary schemes concatenated with Reed-Solomon (RS) codes is investigated over Rayleigh frequency selective and fast time-varying fading channels characterized by high Doppler spreads. Simulation results for the unipolar non-coherent MOK compared with its bipolar coherent counterpart show that the non-coherent MOK performs significantly better in terms of packet error rate at high vehicle velocities. With NC-MOK, a performance gain is achieved as well as a simpler receiver implementation.

In this paper we show how joint demapping for multilevel modulation and source decoding using the BCJR algorithm on a Markov source, reduce the source symbol error rate (SSER), when compared to the subsystems working independently. Simulations demonstrate that at low Eb/Novalues, our proposal performs better than systems that consider source compression and channel coding with short codelength if there is redundancy in the source information to be used. Iterative and joint iterative systems using LDPC, turbo codes or the turbo principle with a convolutional code, show excellent bit error rate performance and approach the Shannon limit as the code length is increased. However, when the size of the code is relatively short, their performance is poor at low Eb/Novalues, becoming worse than the uncoded signal at some points

In this contribution we study and compare the performance of orthogonal frequency code division multiplexing (OFCDM) and multi-carrier direct-sequence code division multiple access (MC-DS-CDMA) based on MMSE multi-user detection (MUD) in single-cell and multi-cell environments for the forward link of a cellular mobile system. The BER and PER results for both systems show that the effect of user loading and modulation scheme on each system varies the performance significantly while changing the spreading factor has no noticeable impact on both system performances.

One approach to maximizing the efficiency of medium access control (MAC) on the uplink in a future wideband code-division multiple-access (WCDMA)-based third-generation radio access network, and hence maximize spectral efficiency, is to employ a low-complexity distributed scheduling control approach. The maximization of spectral efficiency in third-generation radio access networks is complicated by the need to provide bandwidth-on-demand to diverse services characterized by diverse quality of service (QoS) requirements in an interference limited environment. However, the ability to exploit the full potential of resource allocation algorithms in third-generation radio access networks has been limited by the absence of a metric that captures the two-dimensional radio resource requirement, in terms of power and bandwidth, in the third-generation radio access network environment, where different users may have different signal-to-interference ratio requirements. This paper presents a novel resource metric as a solution to this fundamental problem. Also, a novel deadline-driven backoff procedure has been presented as the backoff scheme of the proposed distributed scheduling MAC protocols to enable the efficient support of services with QoS imposed delay constraints without the need for centralized scheduling. The main conclusion is that low-complexity distributed scheduling control strategies using overload avoidance/overload detection can be designed using the proposed resource metric to give near optimal performance and thus maintain a high spectral efficiency in third-generation radio access networks and that importantly overload detection is superior to overload avoidance.

This paper compares the performance of the predistortion and postdistortion compensation techniques in the context of a radio-over-fiber link. The results show that postdistortion offers more advantages than predistortion, and hence it is proposed for direct laser modulation in cellular radio-over-fiber applications. Mathematical analysis has been verified with results from simulation studies.

Call admission control (CAC) is an essential part of radio resource management in wireless communications, where CAC algorithms are employed to provide quality of service (QoS) [3GPP, 1999] and efficient radio resource utilization in 3rd generation radio access networks (3GRAN). This paper presents a novel radio resource reservation scheme that uses the normalised-power resource metric, to guarantee minimum capacity operating points for different services according to their resource requirements.

A new method for the stabilization of the slotted ALOHA protocol is presented in this paper. The approach is based on a modified stochastic gradient adaptation equation that updates from time-slot to time-slot the permission probability parameter that limits the load going onto the channel. Tested in the context of the simple slotted ALOHA protocol and then extended to a spread slotted ALOHA system, the new method achieves a near optimal performance with a substantially reduced complexity, as compared to other stabilization methods.

In this paper, the co-existence issue between IEEE 802.11g wireless-local-area networks (WLANs) and Bluetooth (BT) devices is examined and the use of symbol erasures to reduce the impact of this interference source is proposed. The minimum signal-to-interference ratio (SIR) required by an 802.11g WLAN to achieve a target PER of 0.01 with the number of erasures as a parameter is examined. From these SIR values, the coverage of the WLAN access point (AP) when the wireless station (STA) is being interfered by a BT device is studied. Simulation results show that at a high operational E/sub b//N/sub 0/ = 30 dB, the WLAN's maximum coverage reduces by half as the data rate increases from 6 Mbps to 54 Mbps. The use of symbol erasures significantly enhances the coverage from 250% to 900% and from 40% to 300% when a BT device is 1 m and 10 m away from the STA, respectively. However, there is a threshold for the number of erasures beyond which further improvements in system performance are not obtained.

A new method for generating families of ternary spreading sequences is presented. The sequences have aperiodic zero correlation zones and large families are created for a specific sequence length. The sequences are proposed as spreading sequences to provide high capacity and cancel multipath and multiple access interference (MAI) in a single carrier (SC) or multicarrier (MC) direct-sequence code division multiple access (DS-CDMA) system. A multicarrier DS-CDMA system is simulated that employs the new sequences as spreading sequences in a multipath channel. Bit error rates (BER) and frame error rates (FER) for a range of E/sub b//N/sub 0/ values are presented and it is demonstrated that the proposed sequences improve the BER and FER performance when used in place of masked Walsh codes for the frequency selective fading channel evaluated, when a single correlator receiver is used on each sub-carrier.

In this work we introduce the concept of random early detection (RED) to a medium access control (MAC) protocol applicable to the W-CDMA UMTS access interface. The concept is in general applicable to MAC protocols that use channel load information to regulate the access to a CDMA channel. By making the analogy of a CDMA channel as if it were a queuing system of certain capacity, RED prevents the onset of outage due to multiple access interference, in the same way that it prevents a burst of packet losses in an IP buffer. As a result, a substantial improvement in the stability of the protocol is achieved, for a wide range of input traffic loads.

An investigation on mixing real-time and non-real-time services in UTRA is presented. The main objective of this work is to observe and understand how service characteristics of bit-rate, mean connection duration, required E/sub b//I/sub 0/ and delay tolerance, influence the performance of radio resource management (RRM) in supporting mixed real-time and non-real-time services.

The application and performance of a blind adaptive algorithm in a DS-CDMA communication system is considered. The proposed blind algorithm is a stochastic gradient-based algorithm derived from the standard least mean square (LMS) adaptation algorithm. The algorithm is blind in the sense that information of other users such as the timing, channel information and not required. We demonstrate the convergence of the blind algorithm in the mean square error (MSE) sense and derive its steady state MSE. The bit error rate (BER) and MSE performance of the proposed blind algorithm in an asynchronous system are presented.

The performance of an infrared wireless spread spectrum system using biorthogonal codes under the effect of multipath dispersion is evaluated through theoretical analysis and computer simulations. The performance of the system with (i) biorthogonal Walsh codes and (ii) biorthogonal random codes are investigated in a simulated non-directed line-of-sight infrared channel. An approximation to the bit error probability is derived by using a Gaussian approximation for the intersymbol interference due to multipath propagation. The average probability of error as a function of signal-to-noise ratio is used as the performance criteria. Results show that a biorthogonal spread spectrum system is able to combat the effect of multipath dispersion since only small power penalties are incurred while increasing the system spectral efficiency. It is also observed that biorthogonal Walsh codes have a slightly worse performance than random biorthogonal codes in a less dispersive channel. However, the former has superior performance than the later in a more dispersive channel. Comparison of the analytical and simulation results show that the Gaussian approximation becomes more accurate in less dispersive channels and when the length of the code sequence increases.

Indoor wireless infrared transmission is severely impaired by noise and interference produced by artificial ambient light. The interference produced by fluorescent lamps driven by electronic ballasts causes very large power penalties. In this paper spread spectrum techniques are proposed to combat the penalties caused by artificial light interference. Analytical, simulation and experimental results of bit error rate versus signal-to-noise ratio are presented for a 1 Mb/s spread spectrum wireless infrared system. The results show that spread spectrum techniques reduce the degradation due to artificial light interference.

Much of the current work on medium-access-control (MAC) for wireless, multimedia communications focuses on statistically multiplexing traffic over a single high-speed channel, e.g. the dynamic-slot-assignment (DSA) protocol. However, fundamental queuing theory suggests that a MAC strategy which statistically multiplexes traffic over multiple parallel channels will offer smaller channel-access delays. Therefore, we present a novel slotted CDMA-based MAC protocol for the support of real-time, delay-sensitive multimedia traffic in wireless LANs. The channel-access delay performance and throughput performance of the proposed protocol are investigated, and the results show that the proposed protocol offers both a superior channel-access delay performance to that offered by DSA and a considerable throughput advantage when compared with ALOHA DS/SSMA ('random access' CDMA). A fair method for normalising throughput and delay of CDMA-based MAC protocols when compared with other dissimilar schemes is also presented.

The matched filter detector (MFD) is sub-optimal in DS/CDMA communications systems due to the presence of multiple access interference. This leads to a significant decrease in BER performance and hence system capacity. Multi-user detectors have been proposed to combat this problem but at the expense of a considerable increase in detector complexity. The optimum single-user detector (OSD) is presented, which, for a modest increase in complexity compared with the MFD, achieves MAI cancellation and hence improved BER performance over the MFD. A study of the auto-correlation matrix, R/sub a/, leads to detector designs which perform MAI cancellation for both synchronous and asynchronous systems.