Ergodic Spectrum Management (ESM)'s basic features are introduced as a cloud-based management of wireless connectivity that targets improvement of internet-user's quality of experience. Ergodic Spectrum Management (or ESM) learns and exploits near-ergodicity, or time-consistency, to improve a communication-link connection's stable and efficient use in time, space, and frequency; while using consumer quality of experience as the target metric. ESM methods can also improve existing radio resource management, particularly advancing unlicensed spectrum-use efficiency to levels at or exceeding those associated with licensed spectra, as shown herein. ESM's use of learned probability distributions' dimensional (time, space, and frequency) consistencies enables latency-insensitive remote-cloud-based resource management to be applied to wireless multi-user transmission. ESM methods are developed for 3 increasingly more effective stages that correspondingly increasingly rely on data collection and functional-profile (policy) guidance of physical-layer design choices. ESM application to either and both of existing and future unlicensed- and licensed-spectra networks is suggested as a means to improve overall wireless performance. Examples and field data are provided to show the potential of very large improvements in wireless system connectivity, throughput, and quality of experience.

Wireless-wireline convergence and cellular wireless deployment can economically accelerate through partial transmission of wireless 4G, 5G (generally 3GPP-standards-compliant), and/or Wi-Fi 6 baseband signals on the billions of copper phone, Ethernet, coaxial cable, and other wireline connections. This article poses such a Cellular Subscriber Lines (CSL) re-use architecture and investigates large bandwidth-efficiency gains, as well as the consequent cost-efficiency improvement that accrues for CSL's deployment infrastructure. In-home wireless signals' seamless distribution partially over copper links can achieve good data-rate-versus-distance profile. Results here also expand to Wi-Fi (possibly with MIMO use) on Ethernet multi-pair cables, finding very large gains over existing enterprise mesh (ad-hoc or otherwise) approaches.

This paper considers the problem of interference channel (IFC) with overlay cognitive radio setting. Both achievable rate and outer bounds for an overlay cognitive radio channel are developed, where the cognitive transmitter has partial knowledge of the legitimate transmitter's message. Specifically, an IFC setting is considered where one transmitter (the “cognitive” one) knows the message of the other (“legitimate” transmitter) partially. An outer bound on the capacity region of this channel is found for the “weak” interference case (where the “interference” caused by the cognitive transmitter to the legitimate receiver is weaker than the “signal” from the cognitive transmitter to the cognitive receiver). This outer bound is developed for the discrete-memoryless case and evaluated for a Gaussian channel setting. An achievable region is subsequently determined for a partially cognitive radio channel, and the outer bound on the capacity region is compared with the achievable rate in a Gaussian channel. Subsequently, an achievable region that incorporates elements of the Han-Kobayashi coding strategy with dirty paper coding is developed for this channel.

This paper considers the problem of cognitive radios with partial message information. Here, an interference channel setting is considered where one transmitter (the ldquocognitiverdquo one) knows the message of the other (ldquolegitimaterdquo user) partially. An outer bound on the capacity region of this channel is found for the ldquoweakrdquo interference case (where the interference from the cognitive transmitter to the legitimate receiver is weak). This outer bound is shown for both the discrete-memoryless and the Gaussian channel cases. An achievable region is subsequently determined for a Gaussian partially cognitive-radio channel. The achievable strategy described in this paper is a combination of superposition and dirty paper coding.

The throughput of an IEEE 802.11 network decreases as the number of users increases because of the increased collision probability. To improve the throughput in the presence of a large population, this paper presents an opportunistic carrier-sense multiple-acces/collision-avoidance (CSMA/CA) scheme that exploits multi-user diversity while minimally modifying the IEEE 802.11 medium-access control. This method prioritizes those users having high signal-to-noise-ratio by granting earlier access to these users, thus improving the throughput. This prioritization, however, can cause repeated collisions of same users, which is similar to so-called head-of-line (HOL) blocking. To reduce the probability of the occurrence of the HOL blocking, a simple randomization is proposed. A probabilistic analysis shows that this scheme significantly reduces the HOL blocking probability. The simulation results show that the proposed method improves the throughput by as much as 100%, while achieving long-term fairness among users with different channel conditions.

This paper proposes a method that reduces transmit-power consumption of carrier-sense multiple-access (CSMA) networks by utilizing multiuser diversity and power control. Using this method, a terminal sends a packet at a slot if the terminal's signal-to-noise ratio (SNR) is above the threshold associated with the slot. Since the threshold value decreases as time advances, this method will make the user with the largest SNR access the shared channel; thus, a packet can be transmitted with less transmit power. The analysis under the infinite-user model shows that, as traffic load grows, the expected sum-power of the conventional CSMA network increases whereas that of the proposed method decreases.

This paper investigates the unequal allocation of margin across tones in a multicarrier communication system. Using empirical statistics of the channel signal-to-noise-ratio variation, an algorithm is developed for modems to optimally distribute the available margin across tones instead of allocating equal per-tone margins. Such unequal per-tone margin allocation results in better stability of the line in terms of the outage probability especially when bit and energy adaptation mechanisms are not available or respond slowly to changes in the channel or noise spectrum.

This paper investigates the optimization of margins in digital subscriber lines employing level-2 dynamic spectrum management, where lines are jointly optimized with an emphasis on their stability, throughput-guarantee, and politeness. A new definition of noise margin and the concept of probability of outage are introduced, which allow for an easier formulation of the problems of joint margin and spectra optimization of the lines taking into account their stabilities. The solutions to the highly-coupled optimization problems are simplified using noise margins instead of signal-to-interference-and-noise-ratio margins. The presented algorithms provide up to 100% improvements in the data-rates or a reduction in the probability of outage by an order of magnitude, thus improving the stability of the lines at high data rates.

This paper investigates the optimization of margins in a digital-subscriber-line (DSL) system employing level-1 dynamic spectrum management. A central spectrum management center determines the empirical statistics of the noise variance of each DSL line using long-term observations and optimizes the margin allocation using the statistics. Compared to current systems that allocate ad-hoc margin values, the presented algorithms improve the line's stability, throughput-guarantee, and politeness to other lines in the binder.

This paper proposes to use flexible adaptive- modulation-and-coding (AMC) tables in a wireless network. To support the flexibility of AMC tables, a low-complexity AMC table optimization algorithm is also proposed. The proposed algorithm iteratively optimizes the switching levels of an AMC table according to channel environments, and has fast convergence speed. Computer simulation results show that the proposed algorithm optimizes AMC tables according to different cell characteristics, and that using flexible AMC tables for a wireless network achieves near-optimal average spectral efficiency even with a small feedback load.

Since many random-access protocols are designed based on the assumption that all terminals follow the same medium-access-control (MAC) policy, they can be vulnerable to the selfish behavior of each terminal. This paper proposes robust random-access protocols for wireless networks in fading environments, where each terminal operates in a Nash equilibrium (NE) of a random-access game. Since any deviation of a terminal from an NE penalizes the terminal, the network with this protocol becomes more robust by preventing a selfish terminal from violating the access protocol. We model slotted ALOHA and carrier-sense multiple access (CSMA) as games and show that the strategies in symmetric equilibria of these games have the properties so that a terminal with a better channel state is more likely to access the channel. Thus, these protocols ensure multiuser diversity as well as robustness, a conclusion confirmed by numerical results.

Multicarrier modulation partitions an inter-symbol interference channel into multiple narrowband channels if the length of the cyclic prefix is longer than the channel impulse response. Otherwise, interference from the current and previous multicarrier symbols causes significant distortion at the receiver. This paper expands on the approach introduced in (K.-W. Cheong et al., 1998), where a transmitter based precoder suppresses insufficient-cyclic-prefix distortion. In this paper, the problem of finding an approximate optimal linear precoder to maximize the data-rate in the presence of inter-carrier interference (ICI) due to insufficient-cyclic-prefix distortion is formulated and shown to be a convex optimization problem. The paper further explores low-complexity transmitter equalization and joint transmitter-receiver processing schemes. The proposed methods result in a novel low-complexity insufficient-cyclic-prefix distortion reduction algorithms to maximize the data-rate.

A user-identity feedback method is proposed to achieve multi-user diversity in broadcast channels. This method associates the feedback slots with pre-determined thresholds that diminish with time, and allows feedback from those users whose channel states exceed the threshold assigned to the current slot. Since the threshold can approximate the channel state, this method requires only user-identity feedback. In Rayleigh fading channels, this method is mathematically shown to achieve the sum-rate capacity asymptotically with a large number of users, while requiring only a few feedback slots and little transmission power.

In slow-fading uplink channels, carrier-sense multiple-access (CSMA) has been a popular random-access method, although it can have increased the throughput by using channel state information (CSI) acquired from a downlink training signal and electromagnetic reciprocity. To improve the throughput by using the CSI, this paper presents a random- access scheme that achieves multi-user diversity, called opportunistic p-persistent CSMA (OpCSMA). A user using OpCSMA sends a packet in a slot if the user's CSI exceeds the threshold assigned to the slot. The thresholds diminish with time to prioritize users having good CSI, while being designed to maintain the same persistency as the conventional CSMA, thus enabling backward compatibility. OpCSMA is mathematically shown to significantly increase the throughput compared with conventional CSMA, when the infinite-user model is used to model the variation of the number of users. As the expected number of users increases, the expected sum-rate of the OpCSMA approaches that using a centralized scheduler, which is the theoretical upper bound.

The throughput of an IEEE 802.11 network decreases as the number of users increases because of the increased collision probability. To improve the throughput with a large population, this paper presents an opportunistic CSMA/CA scheme that exploits multi-user diversity, while maintaining backward compatibility with the IEEE 802.11 medium access control. This method prioritizes those users having high signal-to-noise-ratio by granting earlier access to these users. A simple randomization is proposed to prevent the repeated collisions of same users caused by this prioritization. The simulation results show that the proposed method improves the throughput by as much as 100% with a large population.

This paper considers energy minimization for a fast-fading random-access network, where each user sends a single fixed-length packet by selecting a single time-slot within a strict delay-limit. The proposed algorithms assume that each user causally knows its channel state information from electromagnetic reciprocity. With the channel distribution known to all users, the proposed dynamic-programming solution provides an optimal scheduler that minimizes the sum of energy used to transmit a packet and outage cost incurred by a packet drop. Without the knowledge of the channel distribution, a heuristic scheduler is additionally proposed, which learns channel statistics by observing initial time slots.

Multicarrier modulation partitions an inter-symbol interference channel into multiple narrowband channels if the length of a cyclic prefix is longer than the channel impulse response. Otherwise, interference from the current and previous symbols cause significant distortion at the receiver. This paper proposes a low complexity approach to efficiently suppress this distortion by reserving a few tones. While the interference from the previous symbol is canceled by the receiver using the already detected symbol, the interference from the current symbol is suppressed at the transmitter by appropriately correlating transmit data tones and the reserved tones. This correlation and tone reservation cause a small data-rate loss depending on the severity of the channel conditions but overall the proposed scheme will lead to an improved performance.

In a slowly time-varying fading broadcast channel, a proposed randomized scheduler achieves multi-user diversity gain while reducing the amount of feedback. The scheduler requests feedback of signal-to-noise ratios (SNR) from a random subset of users in conjunction with the previously scheduled user, and then selects the user with the largest SNR. With temporal correlation, this scheduler achieves near optimal sum-rate even with feedback from a small subset of users, which considerably reduces the amount of feedback.

This paper considers a multiple-access channel with two state components, where the first sender knows only the first state component, the second sender knows only the second component, and the receiver knows both components. The notion of adaptive-rate capacity is introduced to characterize the set of achievable rates when the state is fixed in each transmission block but can vary between blocks. Single-letter characterizations of the adaptive-rate capacity region for the discrete-memoryless and the Gaussian models are established. The expected adaptive sum-rate capacity is compared to the ergodic sum-rate capacities when the senders have complete and partial state information, and to the sum-rate capacity of the compound MAC. This comparison shows that the adaptive sum-rate capacity can be close to the ergodic capacity and much higher than the sum-rate capacity of the compound MAC.

This paper presents an opportunistic feedback (OF) protocol that achieves the asymptotic sum-capacity of the fading broadcast channel (BC) with a limited amount of feedback. The OF protocol associates a channel value instead of a user to each feedback slot. The users access the slots opportunistically based on their channel state measurement. This allows the base-station to deduce the channel state from the slot index without explicit channel-state feedback. This protocol is then extended to the MIMO BC by using zero-forcing beamforming and random beamforming. The OF protocol is analytically shown to (a) require finite number of feedback slots upper bounded by a small number, (b) be fully distributed, (c) need minimal transmission energy during feedback and (d) asymptotically achieve the sum-capacity of the MIMO BC. Comparison with other opportunistic feedback schemes shows that the proposed scheme has substantially larger sum-rate with a lower feedback overhead.

In this paper, Opportunistic p-persistent Carrier Sense Multiple Access (OpCSMA) is proposed to incorporate multiuser diversity into p-persistent CSMA. In the OpCSMA, each mobile terminal (MT) is assumed to have the knowledge of its channel state information (CSI). At each idle time slot, an MT sends a packet if the corresponding channel gain is above the threshold, which is determined such that the probability of accessing the medium is maintained to be p for any idle slots. Using the infinite user model, it is proved that the OpCSMA provides significant increase in the expected capacity compared to p-persistent CSMA. In addition, the expected capacity of the OpCSMA is shown to be proportional to ln G at low SNR where G is the offered load. Simulation results corroborate the above findings in slow fading channels.

This paper proposes a power efficient p-persistent Carrier Sense Multiple Access (CSMA) employing multiuser diversity, called Opportunistic p-persistent CSMA (OpCSMA). At each idle time slot, an MT sends a packet if the corresponding channel gain is above the threshold which is determined such that the probability of accessing the medium is p for any idle slots. Also, the transmit power is controlled to maintain the constant signal-to-noise-ratio when the channel gain exceeds the cut-off fade depth. The analysis under the infinite user model shows that as traffic load grows, the transmit power consumption of the conventional p-persistent CSMA increases, whereas that of the OpCSMA decreases owing to multiuser diversity effect. Simulation results corroborate these findings in slow fading channels.

Maximum-likelihood (ML) channel estimation for multiple-input-multiple-output (MIMO) channels is derived when orthogonal frequency division multiplexing (OFDM) is employed in cellular systems. While conventional single-cell ML estimation (SCMLE) disregards the effects of inter-cell interference (ICI), multi-cell ML estimation (MCMLE) exploits the knowledge of the preambles from neighboring base stations (BSs) to combat severe ICI. The mean square error (MSE) of the MCMLE is smaller than the conventional SCMLE at the cell boundaries where signal-to-interference ratio (SIR) is about 0 dB. However, the MCMLE performs worse than the SCMLE when the mobile station (MS) is near BS because the MCMLE estimates more parameters than the SCMLE. In addition, we evaluate the influence of non-ideal preambles to the performance of channel estimation because all the preambles in cells cannot be mutually orthogonal in practice. Numerical results confirm the superiority of the MCMLE to the SCMLE when SIR has a range of 0/spl sim/15 dB.

We develop differential space time block codes (STBC) using non-constant modulus constellations for four transmit antennas. The proposed method improves on the conventional differential STBC techniques because of the larger minimum distances of non-constant modulus constellations. The transmitted signals are modulated using pulse amplitude modulation (PAM). Encoding is similar to that of the conventional differential STBC, while the receiver is different. The signal at the receiver is divided by the estimated channel power and then decoded using a conventional QAM decoder which treats pairs of transmitted PAM symbols transmitted from two transmit antennas as one QAM symbol. For transmission rates greater than 2 bits/channel use, the proposed method outperforms the conventional differential STBC.

This paper proposes a low-complexity space-frequency bit-interleaved coded modulation (SF-BICM) transceiver with successive interference cancelling (SIC) processing for multiinput multioutput (MIMO) orthogonal frequency division multiplexing (OFDM) system. Two schemes are presented in order to improve the detection performance of SF-BICM perturbated by the error propagation at SIC receiver. First, the bit stream to each transmit antenna is distributed via the rate-compatible puncturing (RCP) such that the SIC process is "code-assisted". Second, a simple heuristic soft bit-metric computation is proposed to compensate for the incorrect soft information caused by the error propagation. Simulation results in the indoor wireless local area network (WLAN) channels show that the proposed RCPC SF-BICM with the new soft bit-metric has significant power gains up to 6dB over the conventional SIC receiver.

This paper presents recursive construction of Golay complementary sequences in order to give a flexibility to GCS length and the constellation. The recursive constructions for QPSK-GCS, 8PSK-GCS, and 8QAM-GCS have upper bound (3 dB) of PAPR and the constellation aggregation of 8-PSK and 8-QAM constitutes 16-QAM. The GCS are applied to orthogonal frequency division multiplexing (OFDM) systems to design the channel code providing both error correction capability and to generate the training sequence with low PAPR.

In multicast orthogonal frequency division multiplexing (OFDM) systems, the difference in link conditions of users complicates adaptive modulation because modulation should be adjusted to serve the user who experiences the worst channel condition. If we assume that the multicast data are separated into layers and any combination of the layers can be decoded at the receiver, the network throughput can be increased by performing subcarrier/bit allocation. In this paper, in order to increase network throughput, we develop the optimum subcarrier/bit allocation method that maximizes the sum of data rate of all the users employing integer programming (IP) which is NP-hard problem. To reduce the complexity, suboptimum two-step algorithm is proposed: firstly, subcarriers are allocated to users under the assumption that the same power is distributed to each subcarrier; in the second step, the number of bits loaded to each subcarrier is determined using the modified Levin-Campello algorithm. Numerical results show that the performance difference between the optimum and suboptimum algorithms is within about 5%, and that total throughput of the proposed algorithm is larger than that of the lowest channel gain (LCG) method where modulation is determined to serve the user with the lowest channel gain.

A maximum-likelihood (ML) channel estimation and preamble design rules for the multiple-input-multiple-output (MIMO) channels are described when orthogonal frequency division multiplexing (OFDM) is employed with null subcarriers at both DC and high frequencies. The ML channel estimator in the time domain is derived assuming the knowledge of the maximum length of channel. To reduce the mean square error (MSE) of the estimation, three design rules are proposed: orthogonality between the preambles of different antennas, orthogonality between the circular shifted preamble sequences, and the condition that the number of subcarriers is larger than the maximum length of channel multiplied by the number of transmit antennas. In addition, we prove that the use of Golay complementary sequence (GCS) for preamble limits the peak to average power ratio (PAPR) by 3 dB although there are null subcarriers at high frequencies. Numerical results show that the MSE of the proposed method approaches that of optimum ML estimation when the number of null subcarriers and maximum length of channel are small.

A random beamforming technique for MIMO systems that simultaneously obtains downlink multiuser diversity gain, spatial multiplexing gain, and array gain by feeding back only effective SNRs is described. In addition, power control using waterfilling is employed to improve the throughput of our method. In a slow fading channel, we prove that the throughput of the proposed method converges to that of eigen beamforming when many users are in a cell. The number of users required to achieve capacity bound increases with the number of antennas and SNR. However, the capacity bound is achieved even with a small number of users, e.g. 16 users is a cell, when the SNR is low, e.g., 0 dB, and the number of transmit and receive antenna is small, e.g., 2.

We develop a method to puncture a space-time trellis code (STTC) that increases the code rate at the cost of increasing the frame error rate (FER). In order to minimize the FER, the puncturing pattern and constituent convolutional codes that preserve the diversity gain for the short error sequences are presented. The rate 4/3 and 8/7 punctured STTCs achieve two-level diversity gain when the constraint length is five and the frame size is 16. However, the punctured STTCs require 1.3 dB and 0.7 dB more power to attain the same FER as the STTC without puncturing, respectively.

The propose differential space time block codes (STBC) using quadrature amplitude modulation (QAM), which can not be utilized in the conventional differential STBC. Since QAM constellations have a larger minimum distance compared with phase shift keying (PSK), the proposed method has the advantage of SNR gain compared with conventional differential STBC. The QAM signals are encoded in a manner similar to that of conventional differential STBCs. To decode QAM signals, the signals received are normalized by the channel power estimated forgoing training symbols, and then decoded with a conventional QAM decoder. When the transmission rate is more than 3 bits/channel use in time varying channels, the simulation results demonstrate that the proposed method with the channel power estimation outperforms the conventional differential STBC.

The time-domain channel estimator is compared with the frequency-domain channel estimator when multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) is employed. The time-domain maximum likelihood channel estimation (TMLE) and its mean square error (MSE) are derived assuming the knowledge of the maximum channel length. If we use only one OFDM symbol for the estimation, the preamble sequence of each transmit antenna uses a different set of subcarriers in MIMO-OFDM systems. As a result, the MSE of the frequency-domain least square channel estimation (FLSE) is derived assuming that linear interpolation is employed, numerical results show that the MSE of TMLE is smaller than that of FLSE and that the performance difference increases as the number of transmit antenna increases.

A random beamforming technique for multiple-input multiple-output (MIMO) systems that simultaneously obtains downlink multiuser diversity gain, spatial multiplexing gain and array gain by feeding back only effective signal-to-noise ratios (SNRs) is described. In addition, power control using waterfilling is employed to improve the throughput of our method in correlated channels. In a slow fading channel, we prove that the throughput of the proposed method converges to that of eigen beamforming when many users are in a cell. The number of users required to achieve capacity bound increases with the number of antennas and SNR was determined. However, the capacity bound is achieved even with a small number of users, e.g., 16 users in a cell, when the SNR is low, e.g., 0 dB, and the number of transmit and receive antenna is small, e.g., two. We also find that the effect of waterfilling is more noticeable in correlated channels.

We developed a method to reduce peak to average power-ratio (PAR) of multicarrier signals. The method enlarged the quadrature amplitude modulation (QAM) constellation size at a number of tones so that several signal points represent the same information. It chose a signal point among equivalent signal points that minimized PAR. This method achieved more than 4 dB PAR reduction when 64 QAM was used to represent 16 QAM constellation in a 64-subcarrier system. Also we could trade the PAR reduction for complexity and power increase by changing the size of the extended constellation.

We investigate an adaptive modulation method for simultaneous voice and data transmission over fading channels. The proposed scheme applies a different switching threshold-carrier-to-noise ratio (CNR) boundary between different modulation indices-according to the required bit error rate (BER). Specifically, it starts to transmit voice with binary phase shift keying (BPSK) when the CNR allows BPSK transmission with the target BER for voice. When the CNR is improved to support M-ary quadrature amplitude modulation (QAM) with the target BER for data, it begins to transmit both data and voice with the same BER target. Compared with the adaptive hybrid BPSK/M-AM (amplitude modulation) scheme (see Mohamed-Slim Alouini et al., IEEE J. Select. Areas Commun., vol.17, p.837-50, 1999), the proposed method has the same P/sub out/ (outage probability) for voice, and slightly higher P/sub out/ for data. However, the spectral efficiency in high CNR is improved significantly. For example, in a Rayleigh fading channel with an average CNR of 30dB, the proposed scheme is able to transmit about 4.5 bits/s/Hz of data while adaptive hybrid BPSK/M-AM can send only 3.5 bits/s/Hz of data at a BER less than 10/sup -4/.

This paper describes the MetaCore system which is an application-specific instruction-set processor (ASIP) development system targeted for digital signal processor (DSP) applications. The goal of the MetaCore system is to offer an efficient design methodology meeting specifications given as a combination of performance, cost, and design turnaround time. The MetaCore system consists of two major design stages: design exploration and design generation. In the design exploration stage, MetaCore system accepts a set of benchmark programs and structural/behavioral specifications for the target processor and estimates the hardware cost and performance for each hardware configuration being explored. Once a hardware configuration and instruction set are chosen, the system helps generate the target processor design in the form of hardware description language (HDL) along with the application program development tools such as C compiler, assembler, and instruction set simulator. The effectiveness of the MetaCore system was verified with a successful design of MDSP-II, a programmable DSP processor targeted for mobile communication.

This paper describes the MetaCore system which is an ASIP (Application-Specific Instruction set Processor) development system targeted for DSP applications. The goal of MetaCore system is to offer an efficient design methodology meeting specifications given as a combination of performance, cost and design turnaround time.