Indoor environments present significant challenges for wireless connectivity. Public Mobile Network Operators (MNOs) utilizing outdoor macro base stations (BSs) to serve indoor customers suffer from poor signal penetration while indoor Wi-Fi networks may face reliability issues due to spectrum contention. Shared spectrum models, particularly the Citizens Broadband Radio Service (CBRS) band utilized by private 4G/5G networks, have emerged as a promising alternative to providing reliable indoor service. Moreover, these private networks are equipped with the neutral-host (NH) model, seamlessly offloading indoor MNOs’ traffic to the private CBRS network. This paper presents a comprehensive, real-world performance evaluation of three co-located technologies utilizing mid-band spectrum (1–6 GHz): a CBRS-based NH network, public MNO macro net-works, and a Wi-Fi 6 network, inside a large, big-box retail store characterized by significant building loss. While the evaluation is site-specific, it is a real-world representation of a highly dense class of indoor deployments. Our analysis demonstrates: (i) the NH network provides superior indoor coverage compared to MNO macro, requiring only six CBRS devices (CBSDs) versus 65 Access Points (APs) for enterprise Wi-Fi to achieve full coverage, with a median building loss of 26.6 dB ensuring interference-free coexistence with outdoor federal incumbents; (ii) the NH network achieves substantial indoor throughput gains, with per-channel normalized throughput improvements of 1.44× and 1.62× in downlink (DL), and 4.33× and 13× in uplink (UL), compared to 4G and 5G macro deployments, respectively; (iii) the NH deployment achieves a median indoor aggregated physical (PHY)-layer DL throughput gain of 2.08× over 5G macro deployments indoors, despite utilizing only 40 MHz of aggregated bandwidth compared to 225 MHz for 5G macro; and (iv) the NH deployment also outperforms Wi-Fi in application-layer HTTP DL performance by 5.05×. The findings offer critical insights by presenting: (i) a framework to leverage real-world deployments as testbeds for studying indoor shared-spectrum networks; and (ii) measurement-based evidence supporting the use of NH to improve indoor cellular coverage.

5th Generation (5G) New Radio Unlicensed (NR-U) enables Mobile Network Operators (MNOs) to extend their network capacity by leveraging nearly 2 GHz of mid-band unlicensed spectrum. However, delivering delay-sensitive services over shared spectrum is challenging due to unpredictable contention delays and variable channel conditions. To address this, the 3rd Generation Partnership Project (3GPP) introduced Channel Access Priority Classes (CAPCs), which allow multiple concurrent Listen-Before-Talk (LBT) processes with varying access probabilities. This design aims to balance diverse Quality-of-Service (QoS) requirements alongside fair access in shared spectrum environments. Traffic classes are mapped to one of the four CAPCs, allowing probabilistic time-domain resource slicing. Mapping complex, multi-dimensional QoS requirements to CAPCs, however, remains a non-trivial task, as no single CAPC optimally supports a given traffic flow under varying channel conditions and QoS demands. In this paper, we propose a QoS-aware scheduler that decouples traffic flows from specific CAPC processes. This scheduler prioritizes flows for each Transmit-Time-Interval (TTI) within a valid Channel Occupancy Time (COT) regardless of which CAPC wins contention. Our experimental results demonstrate over a 50% reduction in average delay for high-priority traffic and more than a 43% delay reduction across all traffic classes using this decoupled scheduling mechanism, achieved without modifying contention parameters. By leveraging NR-U's synchronized slot structure and refined QoS controls inherited from licensed-access frameworks, this approach significantly improves COT utilization and the delivery of delay-critical services.

The measurement of network speed, specifically broadband speed/throughput as measured by tools like iPerf, has long been used as a key performance indicator for home broadband. Unfortunately, home users rarely have the capability to conduct reliable wired tests, instead being only able to measure using Wi-Fi. Hence, home wireless is often viewed as an unreliable indicator of network speed, leaving home users with little recourse to challenge the quality of broadband speed being delivered. To that end, we seek to answer the extent to which such tests are unreliable and, more importantly, to understand if one can accurately determine if the result was indicative of broadband as a bottleneck or if the measurement was limited by Wi-Fi. In our paper, we demonstrate that such a determination is eminently possible and, moreover, such a determination can be done drawing only on features and groups of features already reported by iPerf. We show through extensive experiments that one can capture the goodness (test was indicative of broadband speeds) or badness (test was not indicative of broadband speeds) with a 92. 5% accuracy, drawing only on the median throughput and interquartile range with second-by-second windowing reported by iPerf. Finally, we show that there is a negative correlation between the ratio of Wi-Fi throughput to Ethernet (broadband) throughput and the interquartile range normalized with its corresponding Wi-Fi throughput.

Understanding the real-world end-to-end performance of residential Wi-Fi and broadband networks is essential for consumers, service providers, and policy makers in an increasingly connected society to determine how connectivity can be improved, through better technology or appropriate spectrum decisions. While previous research has studied such performance, the focus has primarily been on the wired Internet, pointing to Wi-Fi as a bottleneck without investigating the reasons thereof. We believe that the preliminary results presented in this paper, from in-depth studies of residential Wi-Fi deployments in a small Midwestern town, offer a first look into how the Wi-Fi environment may impact the user experience. Over a period of six months, we deployed single-board computers to measure the throughput and latency of Wi-Fi and the backhaul broadband network in a number of different residential environments, as well as capture the Wi-Fi signal environment. Our analyses show: (i) interoperability issues between AP and client supporting different Wi-Fi amendments (e.g., 802.11ac, 802.11ax); (ii) a lack of smart interference management and Dynamic Frequency Selection (DFS) support, resulting in over-usage of channels in the U-NII-1 and U-NII-3 bands when other, less congested bands may be available.

Today, Wi-Fi is over 25 years old. Yet, despite sharing the same branding name, today’s Wi-Fi boasts entirely new capabilities that were not even on the roadmap 25 years ago. This article aims to provide a holistic and comprehensive technical and historical tutorial on Wi-Fi, beginning with Institute of Electrical and Electronics Engineers 802.11b (Wi-Fi 1) and looking forward to IEEE 802.11bn (Wi-Fi 8). This is the first tutorial article to span these eight generations. Rather than a generation-by-generation exposition, we describe the key mechanisms that have advanced Wi-Fi. We begin by discussing spectrum allocation and coexistence, and detailing the IEEE 802.11 standardization cycle. Second, we provide an overview of the physical layer (PHY) and describe key elements that have enabled data rates to increase by over 1000×. Third, we describe how Wi-Fi medium access control (MAC) has been enhanced from the original distributed coordination function (DCF) to now include capabilities spanning from frame aggregation to wideband spectrum access. Fourth, we describe how Wi-Fi 5 first broke the one-user-at-a-time paradigm and introduced multi-user (MU) access. Fifth, given the increasing use of mobile, battery-powered devices, we describe Wi-Fi’s energy-saving mechanisms over the generations. Sixth, we discuss how Wi-Fi was enhanced to seamlessly aggregate spectrum across 2.4-, 5-, and 6-GHz bands to improve throughput, reliability, and latency. Finally, we describe how Wi-Fi enables nearby access points (APs) to coordinate in order to improve performance and efficiency. In the Appendix, we further discuss Wi-Fi developments beyond 802.11bn, including integrated millimeter-wave (IMMW) operations, sensing, security and privacy extensions, and the adoption of artificial intelligence (AI)/machine learning (ML).

Robust classification of the operational environment of wireless devices is becoming increasingly important for wireless network optimization, particularly in a shared spectrum environment. Distinguishing between indoor and outdoor devices can enhance reliability and improve coexistence with existing, outdoor, incumbents. For instance, the unlicensed but shared 6 GHz band (5.925 - 7.125 GHz) enables sharing by imposing lower transmit power for indoor unlicensed devices and a spectrum coordination requirement for outdoor devices. Further, indoor devices are prohibited from using battery power, external antennas, and weatherization to prevent outdoor operations. As these rules may be circumvented, we propose a robust indoor/outdoor classification method by leveraging the fact that the radio-frequency environment faced by a device are quite different indoors and outdoors. We first collect signal strength data from all cellular and Wi-Fi bands that can be received by a smartphone in various environments (indoor interior, indoor near windows, and outdoors), along with GPS accuracy, and then evaluate three machine learning (ML) methods: deep neural network (DNN), decision tree, and random forest to perform classification into these three categories. Our results indicate that the DNN model performs the best, particularly in minimizing the most important classification error, that of classifying outdoor devices as indoor interior devices.

The 3.7 - 3.98 GHz frequency band (also known as C-band) was recently allocated in the US for the deployment of 5G cellular services. Prior to this, the lower adjacent band, 3.55 - 3.7 GHz, had been allocated to Citizens Broadband Radio Service (CBRS), where the entire 150 MHz can be used for free by Tier 3 General Authorized Access (GAA) users, under strict authorization of the Spectrum Access System (SAS). However, adjacent channel interference may reduce the performance of GAA and C-band systems due to lack of guard bands and no Time Division Duplexing (TDD) synchronization, i.e., uplink/downlink configurations are not synchronized. In this paper, we quantify the effect of this mutual interference by performing experiments with a real-world deployment. Significant downlink throughput reductions on both systems are observed when two devices are in close proximity to each other, with one is transmitting uplink while the other is transmitting downlink: 60% for 4G CBRS and 43% for 5G C-band. We believe that this is the first paper to demonstrate this in a real deployment. This throughput degradation was reduced when the CBRS base-station (i.e., CBSD) changed its channel and operated 20 MHz away from C-band, essentially creating a guard band between the channels. We also demonstrate the improvement in latency under adjacent channel interference by implementing MicroSlicing at the CBSD. Our results indicate that addressing adjacent channel interference due to the lack of guard bands and TDD configuration mismatch is crucial to improving the performance of both CBRS and C-band systems.

5G-NR is beginning to be widely deployed in the mmWave frequencies in urban areas in the US and around the world. Due to the directional nature of mmWave signal propagation, improving performance of such deployments heavily relies on beam management and deployment configurations. We perform detailed measurements of mmWave 5G deployments by two major commercial 5G operators in the US in two diverse environments: an open field with a baseball park (BP) and a downtown urban canyon region (DT), using smartphone-based tools that collect detailed measurements across several layers (PHY, MAC and up) such as beam-specific metrics like signal strength, beam switch times, and throughput per beam. Our measurement analysis shows that the parameters of the two deployments differ in a number of aspects: number of beams used, number of channels aggregated, and density of deployments, which reflect on the throughput performance. Our measurement-driven propagation analysis demonstrates that narrower beams experience a lower path-loss exponent than wider beams, which combined with up to eight frequency channels aggregated on up to eight beams can deliver a peak throughput of 1.2 Gbps at distances greater than 100m.

LTE-U (LTE-Unlicensed) is designed to coexist with Wi-Fi in the unlicensed band by balancing its duty cycle according to the number of coexisting Wi-Fi access points (APs) it detects. For example, a LTE-U base-station (BS) will reduce its duty cycle from 50% to 33% when it senses an increase in the number of co-channel Wi-Fi basic service sets (BSSs) from one to two. But the problem of detecting how many WiFi BSS' are operating on the channel in real-time, without decoding the Wi-Fi header, still remains. In this paper, we present a novel algorithm that solves the problem by using an autocorrelation (AC) function on the Wi-Fi preamble and setting appropriate detection thresholds to infer the number of Wi-Fi BSSs operating on the channel. Performing auto-correlation on the Wi-Fi preamble is a much simpler operation than decoding the entire Wi-Fi packet, which is what would be needed if one were to decode the MAC header to identify the BSS. We implement and experimentally validate the proposed AC detector and demonstrate that there is a differentiable pattern of AC events between one and two Wi-Fi APs. From the collected AC events, we determine a suitable threshold for a reliable detection of Wi-Fi APs. We show that using an AC threshold of NE= 0.8, we can achieve a probability of detection (PD) of 0.9 with a probability of false alarm (PFA) of less than 0.02. Finally, we demonstrate that the performance of the proposed AC detector is superior in terms of PDand PFA compared with the energy detector (ED).

In this paper, we develop an algorithm, based only on energy detection, to detect the number of Wi-Fi basic service sets (BSSs) operating on the same channel. Such an algorithm can be used by a LTE-U base station (BS) to scale back its duty cycle when coexisting with Wi-Fi on the same channel. According to the LTE-U specification, a LTE-U BS scales back its duty cycle from 50% to 33% when it senses that the number of co-channel Wi-Fi BSSs has increased from one to two. There are two ways that this detection can be done: (a) decoding based, where the LTE-U BS decodes the Wi-Fi packet header to determine the unique Wi-Fi basic service set identification (BSSID) and (b) energy based, where only received energy levels are used to determine the number of Wi-Fi BSSs. The former approach requires an LTE-U BS to implement a Wi-Fi decoder and hence increases complexity, whereas the latter is easier to implement, requiring only an energy detector and appropriate detection thresholds to distinguish between one and two Wi-Fi APs. We analyze the latter approach and experimentally verify the feasibility of an energy detector to reliably distinguish between one and two Wi-Fi APs. In order to do so, we first experimentally determine appropriate detection thresholds using comprehensive measurements in realistic environments, both line-of-sight (LOS) and non-LOS (NLOS). These thresholds are then used to perform hypothesis based detection to devise an efficient algorithm that predicts presence of one or two Wi-Fi BSSs. The performance of the proposed algorithm is evaluated, both theoretically and experimentally, by utilizing two metrics (a) probability of detection ($P_D$) and (b) probability of false alarm ($P_{FA}$). We show that using a threshold of -42 dBm delivers greater than 80% $P_D$ and less the 5% $P_{FA}$ which we verify both theoretically and experimentally. Hence energy based detection is a low-complexity means of determining number of Wi-Fi BSSs to help LTE-U scale back its duty cycle appropriately.

We introduce the concept of using unmanned aerial vehicles (UAVs) as drone base stations for in-band Integrated Access and Backhaul (IB-IAB) scenarios for 5G networks. We first present a system model for forward link transmissions in an IB-IAB multi- tier drone cellular network. We then investigate the key challenges of this scenario and propose a framework that utilizes the flying capabilities of the UAVs as the main degree of freedom to find the optimal precoder design for the backhaul links, user-base station association, UAV 3D hovering locations, and power allocations. We discuss how the proposed algorithm can be utilized to optimize the network performance in both large and small scales. Finally, we use an exhaustive search-based solution to demonstrate the performance gains that can be achieved from the presented algorithm in terms of the received signal to interference plus noise ratio (SINR) and overall network sum-rate.

In this paper we address the issue of association fairness when Wi-Fi and LTE unlicensed (LTE-U) coexist on the same channel in the unlicensed 5 GHz band. Since beacon transmission is the first step in starting the association process in Wi-Fi, we define association fairness as how fair LTE-U is in allowing Wi-Fi to start transmitting beacons on a channel that it occupies with a very large duty cycle. According to the LTE-U specification, if a LTE-U base station determines that a channel is vacant, it can transmit for up to 20 ms and turn OFF for only 1 ms, resulting in a duty cycle of 95%. In an area with heavy spectrum usage, there will be cases when a Wi-Fi access point wishes to share the same channel, as it does today with Wi-Fi. We study, both theoretically and experimentally, the effect that such a large LTE-U duty cycle can have on the association process, specifically Wi-Fi beacon transmission and reception. We demonstrate via an experimental set-up using National Instrument (NI) USRPs that a significant percentage of Wi-Fi beacons will either not be transmitted in a timely fashion or will not be received at the LTE-U BS thus making it difficult for the LTE-U BS to adapt its duty cycle in response to the Wi-Fi usage. Our experimental results corroborate our theoretical analysis. We compare the results with Wi-Fi/Wi-Fi coexistence and demonstrate that LTE-U/Wi-Fi coexistence is not fair when it comes to initial association since there is a much larger percentage of beacon errors in the latter case. Hence, the results in the paper indicate that in order to maintain association fairness, a LTE-U BS should not transmit at such high duty cycles, even if it deems the channel to be vacant.

Millimeter wave (mmW) frequencies are considered to be indispensable for next generation wireless systems, both cellular and Wi-Fi, primarily due to the large amounts of spectrum available in these bands. However, the higher frequency-dependent path loss at these frequencies needs to be overcome by the use of high-gain directional antenna arrays at both transmitter and receiver. Due to the complexity and peak to average power ratio (PAPR) requirements of OFDM, single-carrier is being considered for the physical layer, which brings up the question of appropriate equalization. In this paper we present a simulation study of equalization structures specifically for a mmW outdoor system, using realistic ray tracing simulation software to generate multipath channels depending on the transmit and receive antenna beam-widths. We then compare decision feedback equalization (DFE) with linear equalization (LE) for these channels and show that in an urban multipath environment the use of DFEs can offer significant gains even with very narrow antenna beams, while the gains are smaller in a suburban environment with less multipath.

The IEEE 802.11 specification for Wireless Local Area Networks (WLANs) supports 20 MHz channels utilizing bandwidths up to 160 MHz. However, the support of devices simultaneously transmitting over different, non-overlapping channels, is not specifically addressed. Recently, there has been interest in developing a 802.11 specification for Carrier Grade Wi-Fi which has led to the requirement for solutions with efficient frequency resource utilization that are not currently supported. In this paper we propose a Medium Access Control (MAC) method, called Multi-User Parallel Channel Access (MU/PCA) that enables simultaneous transmission to multiple devices of various bandwidths, while maintaining backward compatibility with 802.11. We present analytical and simulation results demonstrating the throughput gains that can be achieved using the proposed MU/PCA scheme as compared to the current Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) scheme that is used in 802.11.

The IEEE 802.11 specification for Wi-Fi supports 20 MHz channels utilizing bandwidths up to 160 MHz. However, the support of devices simultaneously transmitting over different, non-overlapping channels, is not specifically addressed. Recently, there has been interest in developing an 802.11 specification for next generation Wi-Fi which has led to the requirement for solutions with efficient frequency resource utilization that are not currently supported. In this paper we continue the study of the Multi-User Parallel Channel Access (MU/PCA) scheme that enables simultaneous transmissions to multiple devices of various bandwidths, while maintaining backward compatibility with 802.11ac. We provide detailed physical layer design methods for MU/PCA, and propose several multi-user sub-channel selection algorithms. Finally we present numerical results which demonstrate the potential performance of the proposed MU/PCA algorithms.

Medical Body Area Network (MBAN) technology is a promising solution to improve patient care outcomes and lower healthcare costs. To foster MBAN innovations, the FCC recently allocated dedicated spectrum for MBAN services. In this paper, we present a brief summary of the FCC MBAN rules. Then, we discuss the technical rationale for the selection of key parameters, such as frequency band selection, emission bandwidth limit, and transmission power limit. Finally, we provide link budget analysis and MBAN coexistence simulations to demonstrate that the FCC rules can meet the requirements of MBAN applications.

The availability of Television White Spaces (TVWS) has recently attracted considerable attention in industry and academia. Given the relatively small amount of bandwidth allocated to each TVWS channel (6, 7 or 8 MHz depending on geography), channel aggregation/bonding, which enables simultaneous usage of multiple TVWS channels, is an efficient approach to increasing the data rate. In this paper we compare channel aggregation at the MAC layer with channel bonding at the PHY layer. Three approaches are investigated: MAC layer aggregation, PHY layer bonding and a new proposal called enhanced PHY (ePHY) layer bonding. We present simulation results that show that when the SINR difference between aggregated/bonded channels is large that (i) the PHY performance of ePHY bonding is superior to PHY bonding both in terms of available data rates and PER performance and (ii) for both slow and fast link adaptation methodologies, ePHY bonding and MAC aggregation deliver higher throughputs than straightforward PHY bonding.

In this paper we compare the implicit and explicit methods of providing channel state information (CSI) to the transmitter in a multi-user multiple-input-multiple-output (MU-MIMO) system as specified in the draft specification IEEE 802.11ac [1]. The comparison is made on the basis of both overhead requirements and packet-error-rate (PER) performance. We also propose a hybrid feedback scheme that combines the explicit and implicit feedback methods thus benefiting from more frequent calibration without incurring extra overhead.

In some cases, like the proposed IEEE 802.11ah draft specification, there arises a need to have a short Cyclic Redundancy Check (CRC) code to detect errors on the information bits in the various signal fields. While an optimum CRC of the required length can be chosen for this, in order to minimize complexity it may be desirable to "puncture" an existing CRC generator to reduce the number of parity bits transmitted. In this paper we evaluate puncturing of a CRC-8 generator to generate a 4-bit CRC such that the minimum Hamming distance of the resultant code is 2.

We study methods to improve the performance of transmit beamforming as specified in the draft specification of IEEE 802.11ac [1]. Through numerical analysis of exemplary channel statistics, we propose methods to reduce overhead for Givens decomposition based explicit feedback. We further evaluate the channel estimation performance tradeoff using smoothing, and beamforming. Lastly we propose non-precoded channel estimation for low delay spread channels. Numerical performance of the proposed methods are also presented.

In this paper, we present the concept of cluster-based cooperation in which geographically dispersed neighboring nodes collectively transmit information to a distant receiver in the form of distributed space-time block codes. In this context, a new distributed space-time block code transmission strategy is introduced, which is not constrained by the rigid requirement of perfect decoding among participating nodes, and attains full spatial diversity even if one or all cooperating nodes encounter error in decoding information of each other. We also present a hybrid of direct and multihop transmission strategy in which an intermediate MIMO relay station cooperates with the nodes with single antenna. Numerical analyses of the proposed schemes demonstrate significant performance improvements in comparison to decode-forward and direct transmission schemes.

A new rate-| full-diversity Space Time Block Code for 2 TX has been designed by enlarging the signalling set of quaternions[14]. Power-scaling and constellation- rotation of information symbols have been incorporated in order to extend the signalling set. The proposed coding scheme achieves a 75% rate enhancement in comparison to the traditional Alamouti [3] code for QPSK modulation without requiring any additional system resources, e.g. power or bandwidth. The use of power-scaling and constellation- rotation also guarantee full-rank of codeword difference matrices in the extended set, while maximizing the coding gain and minimizing the transmitted signal peak-to-average power ratio. We propose a reduced-complexity efficient decoding algorithm, which does not result in any loss of useful information in comparison to the full-length ML decoding. The proposed high-rate code can also be utilized to provide unequal error protection to two different levels of source bits and hence, is useful in applications where the notion of unequal error protection supports varying degree of fidelity to source data, for example multimedia communications. Extensions to general M-PSK constellations and code design for more than 2 transmit antennas are straightforward.

In this paper, we propose a simplified MIMO transmission scheme combined with symbol spreading, which can improve system performance without additional bandwidth or power resources under fast Rayleigh flat fading channels. The same scheme can also be viewed as a design of space-frequency codes for MIMO-OFDM systems with large frequency selectivity. The tensor product is used to generate rotation matrices for MIMO systems from well-designed ones that are known for single-antenna systems. Because of the lattice-based structure, sphere decoding can be employed to reduce the complexity of ML decoding while maintaining the near ML performance. Moreover, MMSE receivers can also be used due to the systematic structure at the transmitter. Simulation results have been provided to support good performance of the proposed scheme for uncoded system as well as coded system under IEEE 802.11n channel modeling.

Zero-padded OFDM (ZP-OFDM) systems have recently been adopted in certain wireless systems, such as the multiband-OFDM based WiMedia standard, instead of the more commonly used cyclic-prefix OFDM (CP-OFDM). ZP-OFDM offers potentially superior performance in multipath channels only if more complex equalization, such as minimum-mean- squared-error (MMSE) or least-squares (LS) is performed at the receiver instead of the more commonly used overlap-add (OLA) equalizer. These complex schemes usually involve inversion of a non-diagonal, channel-dependent matrix that cannot be precomputed. In this paper we first develop two simplified algorithms for equalization of uncoded OFDM signals that improve performance in channels with spectral nulls compared to the OLA equalizer. We then develop a novel, iterative metric-calculation method for coded OFDM that with proper initialization requires only two iterations to approach the performance of a LS equalizer, without the need for matrix inversions. Simulation results will be presented to demonstrate the performance of the proposed algorithms.

To exploit the cooperative diversity for wireless relay networks, signal space diversity can be combined with practical cooperative communication schemes. In this paper, we investigate cooperative modulation schemes at the symbol level based on fully decoding received signals at the bit level. We propose a novel decode-remodulate-and-forward (D-ReM-F) cooperative modulation scheme that works well with higher signal constellations when relay is close to source. Capacity analysis based on discrete QAM signal inputs for Rayleigh fading channels has been performed for this scheme as well as for amplify-and-forward (AF) scheme and repetition-based decode-and-forward (DMF) scheme. Simulation results have been shown to support the good performance of such cooperative transmission schemes both in slow fading and fast fading cases.

Throughput is an important performance measure for data communications over wireless links. In this work, we consider joint adaptation of coding rates, modulation modes and level of cooperation for cooperative relaying to maximize the data throughput. We consider five different schemes with joint adaptation based on channel statistics: Direct transmission, conventional multihop, stationary and dynamic coded cooperation, cooperative multihop. We first obtain closed form expressions for the throughputs achieved by these schemes. Considering channel coding and modulation schemes used in wireless local area standard (WLAN) IEEE 802.11, we then compute the best throughputs and provide performance comparisons. Our results show that coded cooperation with adaptation provides substantial improvement over direct transmission and conventional multi- hop. Cooperative multihop enables further improvements over coded cooperation by fully exploiting cooperative diversity as well as rate adaptation and achieves the highest throughput performance among these five transmission schemes. We also observe that to maximize the data throughput in direct transmission and conventional multihop, adaptation for each hop only depends on the channel quality from the transmitter to the receiver. However, in cooperative strategies a system wide optimization is necessary.

Spatial multiplexing of data streams on multiple transmit antennae is a well known means of increasing the data-rate in a bandwidth constrained system. At the receiver, maximum likelihood (ML) detection offers the best performance. However, for large constellations and/or large number of antennae the complexity of the decoder grows exponentially. Sphere-decoding is one suboptimal decoding method that has been proposed to reduce complexity by reducing the size of the search space for determining the optimum transmitted symbol vector. In this paper, we present an alternative approach, using an absolute-value based distance for searching, that keeps the size of the search space the same, but reduces the complexity by reducing the number of multiplications required to evaluate the quantities being compared in the search space. This method has vastly reduced complexity compared to ML. Simulation results are presented with a bit-interleaved coded modulation (BICM) system to show that this method has less than 0.5 dB performance loss as compared to ML detection.

The 5.5 and 11 Mbps modes of the 802.11b wireless local area network (WLAN) standard use a type of modulation known as complementary code keying (CCK). This is a kind of block coded modulation that codes information bits into blocks of 8 QPSK symbols and was originally chosen to deal with small multipath delay spreads on the order of 10-50 ns with Rake receivers. However, 802.11b systems are now being used in home, office and warehouse environments where the multipath delay spread can be much greater - on the order of 200 ns. Such environments require the use of equalizers for acceptable performance. In this paper we present algorithms and implementations for joint equalization and CCK decoding that improve the performance of the system substantially over separate equalization and decoding.

It is well known that one of the main sources of interference in the 2.4 GHz unlicensed band is due to the presence of Bluetooth systems in this bands. Recently, the IEEE 802.11 committee adopted a draft standard called 802.11g that will provide data rates of up to 54 Mbps in the 2.4 GHz band using OFDM as the physical layer (PHY) modulation format. One of the main barriers to actually achieving the high data rates will be the presence of interferers like Bluetooth. In this paper we develop a PHY layer algorithm for simultaneously estimating the multipath channel and interference characteristics and using these estimates in the convolutional decoder in order to improve the system performance in the presence of Bluetooth interference. Simulation results indicate that substantial improvements in 802.11g performances can be obtained by this approach.

A new method of co-channel interference rejection for digital television receivers is presented that uses a different rejection filter from the comb filter that was used in the prototype built by Zenith. This filter is optimized for rejection of co-channel NTSC interference in the presence of white noise and hence suffers a penalty of only 0.4 dB in AWGN as compared to 3.5 dB with the comb. The receiver structure with this filter, including required equalizer and trellis decoder modifications is presented, along with simulation results showing the improvement in performance in co-channel-plus-AWGN interference and hence in coverage area.

The two criteria most commonly used in blind equalization are Sato's (1975) cost function and Godard's (1980) cost function. We analyze a sign-error cost function for real signals which gives an error term that can be viewed as the sign of either the Sato or the Godard error. We show that the conventional definition of equalizer convergence is not suitable for analyzing this cost function. A more realistic definition of convergence for low to medium SNR situations is presented and used to analyze this sign-error cost function. The performance of this cost function is evaluated via simulations and shown to have excellent performance as compared to the Godard cost function, with substantially less complexity.

In December 1996 the Federal Communications Commission (FCC) adopted the Grand Alliance (GA) system as the digital television broadcasting standard for the United States ending a seven-year-long search for a fully digital television standard. MPEG-2 was chosen as the video compression standard, and trellis-coded 8-vestigial sideband (VSB) with a training sequence was chosen as the transmission standard. The laboratory tests that were performed on the final two competing systems, 8-VSB with training sequence and 32-quadrature amplitude modulation (QAM) with blind equalization, showed a need for blind equalization in dynamic channels that could not be adequately handled by an equalizer training on the training sequence alone. Hence, the final GA system recommended the use of blind equalization in the receiver. In this paper, we describe the U.S. digital television transmission standard as it pertains to the equalization problem, typical transmission channel characteristics and the need for blind equalization in terrestrial television receivers.

The paper first shows the equivalence of the Bernoulli-Gaussian impulse noise model in the discrete time domain to the continuous-time model of Poisson arriving delta functions with random area distributed according to the power Rayleigh probability density function. This equivalence is then used to develop a closed form expression for the probability of error for single carrier QAM that is easily evaluated. Furthermore, the performance of multicarrier modulation (MCM) is also analyzed using the same impulse noise model and it is shown that in most cases MCM performs better than single carrier systems, specifically when the probability of an impulse is not too high and the impulse power is moderate.