We investigate the beamforming performances of holographic surfaces implemented as arrays of densely deployed, lossy, and identical antennas. We first develop a general model to characterize the mutual coupling effect among the antennas arbitrarily distributed in a holographic surface, and then discuss the beamforming design as well as the characteristic and load impedance optimization of the holographic radio system. CST-based electromagnetic simulations indicate that the proposed beamforming design with impedance optimization significantly increases the realized beamforming gain of a conventional halfwavelength spaced antenna array, and array densification within the same surface aperture further enhances this benefit. The enhancement is particularly noticeable when the target direction is close to the spatial direction in which the array is densified.

In this paper, we investigate the beamforming performance of holographic surfaces implemented as lossless antenna arrays with less than half-wavelength spacing. We first develop a method to quantify the mutual coupling effect among the antennas in an array. The developed coupling model is general and applicable to arrays with arbitrary distribution of any type of antennas with arbitrary structure, physical size and radiation power pattern. In particular, it reduces to a neat analytical expression for arbitrarily deployed isotropic antenna arrays. We then discuss the beamforming design for holographic surfaces, and in particular provide analytical beamforming characterizations for arrays with two arbitrarily spaced isotropic antennas. Numerical results indicate that, by accounting for the mutual coupling effect between antennas, the array densification by packing more antennas in a given surface aperture can significantly enhance both the beamforming gain and spatial resolution of the system. The beamforming gain enhancement and beamwidth reduction can be several dBs higher than, and more than half of, those achieved by the conventional half-wavelength spaced antenna arrays in the same surface aperture. The gains of densification become saturated when the antenna spacing is below a critical value, and the saturated gain reduces as the surface aperture increases.

The rateless multiple access (RMA) scheme is a promising distributed multiple access scheme to achieve simultaneous high reliability, low latency and massive connectivity. In this paper, we investigate the maximum likelihood (ML) decoding performance of the RMA scheme in an Additive white Gaussian noise (AWGN) channel with binary phase-shift keying (BPSK) modulation. For the first time, this paper derives the ensemble weight distribution of the RMA scheme. We derive an upper bound on the decoding error performance of the RMA scheme under ML decoding in an AWGN channel with BPSK modulation. Using the derived bound as the fitness function, we adopt the continuous genetic algorithm to optimize the parameters of the RMA scheme. Simulation results show the tightness of the derived bound and the superiority of the optimized degree distribution over the conventional degree distributions.

We investigate the performances of line-of-sight (LoS) holographic transmission links. To this end, we first develop a simple channel model for LoS holographic radio systems. This model can be reduced to represent the conventional LoS multiple-input multiple-output (MIMO) channel, and further used to make a fair comparison between them. We then analytically show that, in the far-field scenario when both the transmitter and receiver are equipped with holographic surfaces to form a LoS holographic-input holographic-output (HIHO) system, the achievable power gain can be up to π2times higher than the corresponding LoS MIMO system with half-wavelength spaced isotropic antenna arrays deployed in the same transmit/receive apertures. Furthermore, numerical results indicate that concurrent transmissions of multiple signal streams can be supported in both the LoS HIHO and MIMO systems at communication distances shorter than that in the far-field scenario. Specifically, by moving from isotropic antenna arrays to holographic surfaces we virtually keep the same spatial sub-channels as those of the LoS MIMO system but with notably boosted power gains.

Vehicle-to-vehicle (V2V) resource allocation (RA) schemes have been introduced in the cellular V2V (C-V2V) standard for sidelink (SL) communications to allow for an efficient sharing of the time-frequency resources in sub-6 GHz bands. However, the recent progress in connected and automated vehicles and the introduction of new bandwidth-eager mobility services are driving towards the use of millimeter-wave (mmW) frequencies (24.25-52.6 GHz). A characteristic of propagation at mmW frequencies is the severe path loss attenuation that can be compensated through beamforming. Therefore, its introduction adds a spatial dimension that must be considered in the design of RA schemes. The current fifth-generation (5G) RA standard for SL communication, which is inherited from the previous C-V2V standard, is not designed for directional communication and does not take into account the interference impact. Hence, this paper proposes a novel RA scheme to manage spatial-interference by adding the spatial dimension, i.e. the spatial beam directivity, and cooperation between vehicles for resource selection. The simulation results confirm that the three-dimensional cooperative RA (3D-CRA) has an average improvement of 10% in packet delivery ratio, 50% in collision probability, and 60% in channel busy ratio compared to the standard RA.

In this paper, we propose a set of new sounding reference signals (SRSs) for time-division duplexing (TDD) massive MIMO systems with channel aging. It is analytically shown that the proposed set of SRSs exhibit superior zero correlation zone (ZCZ) property, which guarantees sparse and marginal interference between each other. Therefore, all SRSs in the set can be transmitted concurrently in a cell with a short SRS period per user to alleviate the channel aging effect. We also investigate the detailed SRS construction to achieve low peak-to-average power ratios (PAPRs). Finally, simulation results are provided to show that the proposed SRSs result in significantly larger downlink throughput than the existing 5G New Radio SRSs.

In this paper, we propose a set of new sounding reference signals (SRSs) for time-division duplexing (TDD) massive MIMO systems with channel aging. It is analytically shown that the proposed set of SRSs exhibit zero correlation zone (ZCZ) property, which guarantees sparse and marginal interference between the SRSs. Therefore, all SRSs in the set can be transmitted concurrently in a cell with a short SRS period per user to alleviate the channel aging effect. We also analytically derive the peak-to-average power ratio (PAPR) and show how the SRS should be constructed to achieve low PAPR. Finally, simulation results are provided to show that the proposed SRSs result in larger downlink throughput than the 5G New Radio SRSs.

5G physical random access channel (PRACH) will use new preamble formats based on short Zadoff-Chu (ZC) sequences to enable new use cases. These formats result however in a PRACH capacity shortfall where the number of sequences available for network planning may just be enough to support few cells without sequence reuse. To overcome this issue, two enlarged constant-amplitude sequence constructions that include ZC sequences, and thus being backward-compatible with the current 5G PRACH design, are presented. Both constructions feature a desirable subset structure from which follows a natural cellular network sequence allocation where each cell-specific sequence subset has a controllable low-correlation zone similar to ZC sequences, and thus enables a similar detection performance inside a cell. The two extensions are meanwhile structurally different and offer different network allocations, as for one, new sequences are distributed among all cells, while for the other, they are in separated cells. With both proposed supersets and the new 5G PRACH formats, hundred-times more cells without sequence reuse can be supported compared to ZC sequences for a moderately larger inter-cell correlation than intra-cell correlation. Simulation results confirm that using the proposed supersets instead of reusing sequences in the network can significantly improve detection performance.

5G physical random access channel (PRACH) will use several new preamble formats in order to enable new use cases. These new formats, however, results in a PRACH capacity shortfall. In this paper, we propose a solution based on an extension of the LTE PRACH sequence set. Cell-specific sequences are derived from single-root Zadoff-Chu (ZC) sequences with a zero-correlation zone, and if necessary, different m-sequence covers instead of multiple roots as in LTE. While this construction is shown to preserve a similar low-correlation zone as with the LTE design, it does not consume the other ZC roots which can then be used to support more cells. The proposed PRACH design is evaluated by 5G link-level simulations to verify the expected good detection performance and low PAPR.

We propose a secondary synchronization signal (SSS) for the fifth generation (5G) New Radio (NR) communication systems, which is based on the element-wise multiplication of two BPSK modulated m-sequences with different cyclic shifts encoding the physical cell identity (ID) carried by the NR SSS. We present the details on the generator polynomial selection for the involved m-sequences and the mapping between their cyclic shift values and the cell ID. We also propose a double- threshold detection method which is able to mitigate false cell ID detection. Simulation results are provided to demonstrate the superiority of the proposed NR SSS over the LTE SSS. The proposed NR SSS has been accepted in 3GPP Release 15 technical specification.

One of the fundamental problems in cryptography is the generation of a common secret key between two legitimate parties to prevent eavesdropping. In this paper, we propose an information-theoretic secret key generation (SKG) method for time division duplexing (TDD)-based orthogonal frequency-division multiplexing (OFDM) systems over multipath fading channels. By exploring physical layer properties of the wireless medium, i.e., the reciprocity, randomness, and privacy features of the radio channel, an SKG method is proposed to maximize the number of secret bits given a target secret key disagreement ratio (SKDR). In the proposed SKG method, the phase information of the estimated channel state information (CSI) is distilled for SKG, and a special guard band (GB) scheme is designed to achieve the target SKDR with a small phase information loss. The proposed GB consists of both the amplitude GB (AGB) and phase GB (PGB), where the AGB is determined by the average signal-to-interference plus noise ratio (SINR), whereas the PGB adapts itself to the instantaneous SINR and thus incurs a smaller phase information loss in the higher SINR region. Analyses show that this GB scheme trades off a small loss of channel phase information for a better SKDR performance, and achieves a much larger number of quantization levels for a given SKDR due to the fact that the PGB decreases quickly as the SINR increases. Based on the performance analysis on the SKDR, the average secret key length, the phase information loss percentage (PILP), and the optimal GB and quantization level of the adaptive quantizor are derived for a given target SKDR. Both analytical and simulation results are presented to demonstrate the superiority of the proposed scheme for TDD-OFDM systems over frequency-selective fading channels.

In this letter, we develop a low-complexity transceiver design, referred to as semirandom beam pairing, for sparse multipath massive multiple-input-multiple-output (MIMO) channels. By exploring a sparse representation of the MIMO channel in the virtual angular domain, we generate a set of transmit-receive beam pairs in a semirandom way to support the simultaneous transmission of multiple data streams. These data streams can be easily separated at the receiver via a successive interference cancelation technique, and the power allocation among them are optimized based on the classical waterfilling principle. The achieved degree of freedom (DoF) and capacity of the proposed approach are analyzed. Simulation results show that, compared to the conventional singular value decomposition-based method, the proposed transceiver design can achieve near-optimal DoF and capacity with a significantly lower computational complexity.

In this paper, we investigate the optimization of non-uniform linear antenna arrays (NULAs) for millimeterwave (mmWave) line-of-sight (LoS) multiple-input multipleoutput (MIMO) channels. Our focus is on the maximization of the system effective multiplexing gain (EMG), by optimizing the individual antenna positions in the transmit/receive NULAs. Here, the EMG is defined as the number of signal streams that are practically supported by the channel at a finite signal-to-noise ratio. We first derive analytical expressions for the asymptotic channel eigenvalues with arbitrarily deployed NULAs when, asymptotically, the end-to-end distance is sufficiently large compared with the aperture sizes of the transmit/receive NULAs. Based on the derived expressions, we prove that the asymptotically optimal NULA deployment that maximizes the achievable EMG should follow the groupwise Fekete-point distribution. Specifically, the antennas should be physically grouped into K separate ULAs with the minimum feasible antenna spacing within each ULA, where K is the target EMG to be achieved; in addition, the centers of these K ULAs follow the Fekete-point distribution. We numerically verify the asymptotic optimality of such an NULA deployment and extend it to a groupwise projected arch-type NULA deployment, which provides a more practical option for mmWave LoS MIMO systems with realistic nonasymptotic configurations. Numerical examples are provided to demonstrate a significant capacity gain of the optimized NULAs over traditional ULAs.

This paper is concerned with the channel estimation problem in millimetre wave (MMW) wireless systems with large antenna arrays. By exploiting the sparse nature of the MMW channel, we present an efficient estimation algorithm based on a novel overlapped beam pattern design. The performance of the algorithm is analyzed and an upper bound on the probability of channel estimation failure is derived. Results show that the algorithm can significantly reduce the number of required measurements in channel estimation (e.g., by 225% when a single overlap is used) when compared to the existing channel estimation algorithm based on non-overlapped beam patterns.

In this paper, we study the open-challenging problem of antenna selection (AS) at both the relay and source nodes in MIMO two-way relay networks (TWRNs). Two near-optimal algorithms, namely the joint relay-source AS (JRSAS) and the separated relay-source AS (SRSAS), are proposed in a greedy manner. Specially, JRSAS selects antennas at both the relay and source nodes simultaneously in each AS step to maximize the increment of the system throughput. In order to further reduce the AS computational complexity, SRSAS performs AS at the relay and source nodes in two separate stages. Numerical results show that both JRSAS and SRSAS can approach the optimal exhaustive search (ES) AS algorithm but the computational complexity has been significantly reduced.

We study the uplink transmission in multiple-input multiple-output (MIMO) systems with antenna correlation. We focus on schemes that require only channel covariance information at the transmitter (CCIT), which involves lower cost than full channel state information at the transmitter (CSIT). We start from mutual information analysis and show that a simple CCIT-based scheme, referred to as statistical water-filling (SWF), can perform close to the optimal full CSIT-based one in MIMO systems with more receive antennas than transmit ones. We then focus on the implementation of SWF in practically coded systems. An iterative linear minimum mean squared error (LMMSE) receiver is assumed and an extrinsic information transfer (EXIT) chart type curve matching technique is developed based on Hadamard precoding techniques. Simulation results show that the proposed scheme can obtain significant performance improvement compared to the conventional equal power transmission. Finally, we show that the proposed scheme is also very efficient in multi-user uplink MIMO systems with distributed channel information.

This paper considers the rainfall effect on the capacities and achievable rates of millimeter-wave (mmW) multiple-input multiple-output (MIMO) systems. We first develop a new channel model for point-to-point mmW MIMO systems to characterize the rainfall effect. This rain propagation model is derived based on stochastic properties of signal propagation in a general random scattering medium. Under this model, we evaluate the channel capacity of the mmW MIMO system at various rain rates and show that rainfall does not always have a negative impact on the system performance, provided that accurate instantaneous channel state information (CSI) is available at both the transmitter and receiver. We also show that a transmit strategy of statistical water-filling (SWF) allows the mmW MIMO system to have near-optimal performance.

In this paper, we propose a practical transmission scheme using polar coding for the half-duplex degraded relay-eavesdropper channel. We prove that the proposed scheme can achieve the maximum perfect secrecy rate under the decode-and-forward (DF) strategy. Our proposed scheme provides an approach for ensuring both reliable and secure transmission over the relay-eavesdropper channel while enjoying practically feasible encoding/decoding complexity.

In this paper, we study the point-to-point E-band millimeter wave wireless channel with uniform linear antenna arrays (ULAs) deployed at both link ends and present an analytical approach to characterize the channel behavior. We first derive explicit expressions for some channel eigenvalues at certain discrete system settings. The asymptotic behavior and the effective multiplexing distance (EMD) of the E-band channel are then investigated, where the latter is defined as the end-to-end distance at which the channel can support a certain number of spatially independent streams at finite signal-to-noise ratios (SNRs). We analytically show that the EMD for a given number of parallel signal transmissions is mainly determined by the product of the aperture sizes of the transmit and receive ULAs. This finding provides useful insights into the design of practical multi-gigabits wireless communication systems over E-band.

In this paper, we consider a wireless-powered cooperative communication network, which consists of a hybrid access-point (AP), a hybrid relay, and an information source. In contrast to the conventional cooperative networks, the source in the considered network is assumed to have no embedded energy supply. Thus, it first needs to harvest energy from the signals broadcast by the AP and/or relay, which have constant power supply, in the downlink (DL) before transmitting the information to the AP in the uplink (UL). The hybrid relay can not only help to forward information in the UL but also charge the source with wireless energy transfer in the DL. Considering different possible operations of the hybrid relay, we propose two cooperative protocols for the considered network. We jointly optimize the time and power allocation for DL energy transfer and UL information transmission to maximize the system throughput of the proposed protocols. Numerical results are presented to compare the performance of the proposed protocols and illustrate the impacts of system parameters.

In our previous work, a hybrid transform coding (HTC) scheme was proposed for the compression and feedback of channel state information (CSI) in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. In this paper, we investigate the performance of HTC in both the interfering broadcast channel (IBC) model and cellular network model. In IBC, the achievable ergotic rates of HTC are simulated and compared with those of other feedback compression methods. The performance of HTC in cellular networks is also provided based on Long-Term Evolution-Advanced (LTEA) Release 10. The results in both models show that HTC can achieve higher compression efficiency than available alternatives.

This paper studies the fundamental characteristics of point-to-point E-band channels with uniform linear antenna arrays (ULAs) deployed at both the transmitter and receiver. We model the channels as line-of-sight (LoS) multiple-input multiple-output (MIMO) ones and focus on the channel eigenvalue characterization when theRayleigh distance criterioncannot be fulfilled due to limited physical sizes of the transmitter and receiver. We first derive explicit expressions for some channel eigenvalues at certain discrete system settings. Asymptotic analyses are then developed when the antenna numbers at the transmitter and receiver or the distance between them goes to infinity. Based on these analytical results, the maximum eigenvalue and theeffective multiplexing distance(EMD) of the E-band channel are investigated, where EMD is defined as the end-to-end distance at which the channel can support a certain number of simultaneous spatial streams at a given signal-to-noise ratio (SNR). We analytically show that the EMD for a given number of parallel signal transmissions is mainly determined by the product of the aperture sizes of the transmit and receive ULAs. Numerical results are provided to validate the analyses.

In this paper, we investigate a new polynomial pricing function based demand side management scheme for future smart grid, where the consumers are charged based on their instantaneous load. A non-cooperative game is formulated, where each consumer aims to minimize their total energy cost based on the given pricing function. By casting this game in the variational inequality framework, we present sufficient conditions for the uniqueness of the optimal solution. We then propose a distributed and simultaneous algorithm to achieve the optimal solution. Sufficient conditions for the geometrical convergence of our algorithm are also provided and proved. Numerical results reveal that our proposed algorithm converges very quickly, and is effective in encouraging consumers to shift their energy usage from peak to non-peak times.

This paper is concerned with the decentralized power allocation problem in random access systems. We propose a scheme that is especially suitable for systems requiring high throughput but with difficulty in establishing centralized control, such as cognitive radio environments. Specifically, we assume successive interference cancellation (SIC) at the receiver for multi-packet reception (MPR). We consider a decentralized random power transmission strategy where each user selects its transmitted power level randomly according to a power distribution conditioned on its own channel state. Our focus is on the design of this distribution such that the system packet throughput is maximized under rate and power constraints. We start from a two-user system. A main finding of this paper is that the supports of the optimal power distributions are of discrete nature. This finding greatly simplifies the distribution optimization problem. We also discuss a sub-optimal solution to systems with more than two users. Numerical results demonstrate that the proposed scheme can achieve noticeable performance improvement compared with conventional single-user detection (SUD) based ones and offer a flexible tradeoff between the system throughput and power consumption.

In this paper, we consider multi-user multiple-input multiple-output (MIMO) systems over either multiple access channels (MACs) or broadcast channels (BCs). Contrary to common views, we show that antenna correlation at the mobile unit (MU), the base station (BS) or both sides can be potentially beneficial for such systems. Both asymptotic analysis and numerical results indicate that antenna correlation can provide a significant capacity gain in multi-user environments.

This paper is concerned with the efficient feedback of the channel state information (CSI) in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. A hybrid transform coding (HTC) scheme is proposed by exploiting the frequency and time correlation of CSI. An upper bound for the overhead-distortion performance of HTC is derived. Numerical results show that, compared with the available alternatives, the HTC scheme can achieve higher compression efficiency.

This paper is concerned with the advantages of multi-user concurrent transmission in multiple-input multiple-output (MIMO) systems with rate constraints. We first study a maximum eigenmode beamforming (MEB) strategy for fading multiple access channels (MACs). This strategy allows each user to transmit only in its maximum eigenmode direction and applies a suboptimal matched-filter receiver with successive interference cancellation at the base station (BS). We derive a closed-form expression for the average minimum transmitted sum power required by MEB. Based on this, we show that: a) the MEB strategy is asymptotically optimal when the number of simultaneous users is sufficiently large; b) multi-user concurrent transmission has a power advantage, referred to as multi-user gain, over orthogonal transmission approaches such as time-division multiple-access; c) the number of antennas at the BS has a far stronger impact on the system performance than that at each user side. These properties are verified by simulation. Both numerical analyses and simulation results show that a major part of multi-user gain can be achieved in practical environments even with a quite small number of simultaneous users. We also study the MEB strategy for MIMO broadcast channels (BCs). The dirty paper coding (DPC) technique is necessary in this case. It is analytically shown that most observations made for MIMO MACs are extendable to MIMO BCs.

This paper is concerned with the capacity of multiple-input multiple-output (MIMO) cellular systems. We assume an equal rate constraint for all users and adopt a realistic channel model that incorporates path loss, lognormal fading and Rayleigh fading. Several bounds are derived for the minimum transmission power of such rate-constrained MIMO cellular systems with various base station (BS) cooperation strategies. In particular, the upper power bound is based on the maximum eigenmode beamforming (MEB) scheme. These power bounds are then used to obtain the corresponding cellular capacity bounds when partial BS cooperation strategies are adopted. Our results show that, allowing more users to transmit simultaneously, introducing cooperation among BSs and increasing the number of antennas (especially at each BS) are efficient ways to improve system performance.

In this paper, we study the impact of antenna correlation at mobile units (MUs) on the capacity of multi-user multiple-input multiple-output (MIMO) systems with rate constraints. Both numerical results and asymptotic analyses show that antenna correlation can actually be regarded as a beneficial factor for such systems. It is also shown that the maximum eigenmode beamforming (MEB) based interleave-division multiple-access (IDMA) system is an effective platform to exploit the potential gain provided by antenna correlation at MUs.

This paper is concerned with cellular systems with rate constraints in fading environments. We consider a simple but asymptotically optimal matched filtering/successive interference cancellation (MF-SIC) scheme. We derive several concise and closed-form bounds for the power and spectral efficiencies of various base station cooperation strategies, which provide some useful insights into cellular systems.

This paper is concerned with the transmission strategies and relay selection for decode-and-forward parallel relay networks (PRNs) based on superposition coding. Our focus is on the minimization of the aggregate transmission power that supports a given transmission rate. In this paper, two transmission strategies are investigated, i.e., an optimal- cooperation (OC) strategy requiring strict synchronization at the destination/relay nodes and a no-information-overlapping (NIO) strategy with no synchronization requirement for the ease of implementation using current technologies such as interleave- division multiple-access (IDMA). Furthermore, a reduced-relay-selection (RRS) strategy involving only 2-level superposition coding is given to trade off between complexity and performance. Numerical results show that the performance gap between OC and NIO is negligible, and selecting the best two relay nodes is adequate to achieve most performance gain even when the number of relay nodes is large.

In this paper, we study the advantages of multi-user concurrent transmission, measured using the multi-user gain (MUG), in multiple-input multiple-output (MIMO) systems with rate constraints. Our focus is on a maximum eigenmode beamforming (MEB) strategy. We derive a closed-form expression for the transmitted sum power required by the MEB strategy and prove that this strategy is asymptotically optimal. The simple closed-form expression for the MEB sum-power provides many useful insights into the asymptotic behavior of multi-user MIMO systems. Interleave-division multiple-access is adopted as a platform for implementing the proposed MEB scheme. Both numerical and simulation results show that a major part of MUG can be achieved with a quite small number of users.

The recent investigations on interleave-division multiple-access (IDMA) have demonstrated its advantage in supporting high-data-rate and multi-rate services over wireless fading channels. This paper focuses on quality of service (QoS) guarantee in IDMA-based multi-service wireless networks. We propose a QoS architecture which addresses the key issues of QoS guarantee for multi-service in IDMA, including medium access control (MAC), admission control, power control, and rate allocation. The proposed IDMA QoS architecture avoids complex packet scheduling at the MAC layer which is however required in other existing multiple access systems. Data packets can be transmitted in IDMA without scheduling delay. Additionally, to improve the efficiency of random access, an interleave- division slotted-ALOHA (IDSA) access method is proposed for the IDMA MAC protocol. We derive the relationship between the arrival rate of access requests and the number of access interleavers allocated to an IDMA system for a given access success probability. Based on this relationship, we can adaptively adjust the number of access interleavers according to the traffic load of access requests, so as to ensure a satisfactory probability of successful access as well as low complexity of request detection at the receiver.

We consider the sum-power minimization problem for multi-user multiple-input multiple-output (MIMO) systems with rate constraints. We show that significant performance improvements, qualified by multiuser gain (MUG), can be achieved by allowing multiple users to transmit simultaneously on their individual maximum eigenmodes. We also show that a major part of MUG can be achieved even with quite a small number of users and increasing the number of antennas at the base station is an efficient method for maximizing MUG.

This paper is concerned with the power allocation problem for practically coded interleave-division multiple-access (IDMA) systems with iterative multi-user detection (MUD) over multiple access channels (MACs). Both Additive White Gaussian Noise (AWGN) and fading channels are considered. For AWGN channels, two power allocation methods based on linear programming are discussed and compared with an interior-point method (IPM). These techniques are extended to power allocation over fading channels. Numerical results show that, with power optimization, IDMA can achieve significant performance improvements over TDMA in fading environments.