In downlink near-field communication systems, although the conventional maximum ratio transmission (MRT) based beamforming (BF) maximizes the received signal power at the targeted user equipment (UE), it suffers from a beam misfocus problem. That is, the spatially maximum received signal power is achieved not at the desired focal point (DFP), i.e., the targeted UE location, but at a different neighboring location, which causes severe power pollution to neighboring UEs. An iteration-based BF (Iter-BF) method has been proposed to solve this problem, which, however, involves complicated numerical search and fails to achieve a valid solution when the DFP is beyond the so-called feasible focal region (FFR). In this paper, we first derive a closed-form characterization for the FFR of a uniform linear antenna array (ULA), and then develop a new and analytical BF design, referred to as the derivative-based BF (Deri-BF), to solve the beam misfocus problem for arrays with an arbitrary antenna distribution. Numerical results show that for a DFP within the FFR, the proposed Deri-BF achieves a higher received power than the Iter-BF at the DFP. While for a DFP beyond the FFR, the Deri-BF is still able to achieve beam focusing exactly at the DFP, which is unattainable by the Iter-BF.

In this paper, we investigate the impedance matching problem for realistic arrays of lossy and mutually coupled antennas, aiming to enhance the beamforming performance of the system. We develop a novel method to optimize the characteristic and load impedances in the transmit circuit that drives the antenna array. Numerical results are provided to show that the developed method has a faster convergence speed with considerably lower computational complexities than an existing impedance optimization method, while it can achieve almost the same favorable performance as the latter.

We consider massive grant-free random access in a massive multiple-input multiple-output (mMIMO) system. Users transmit a preamble selected at random from a pool, together with data in a grant-free manner. While superposed users with different preambles can be separated and their data decoded, colliding users selecting the same preamble may not be separated. We introduce a preamble collision resolution mechanism, where the multiuser channel of colliding users is resolved with a combination of preamble-based and data-aided channel estimation. For this, we use the sample covariance matrix of the data to estimate the superposition channel from the preamble. For the most likely case of two colliding users, based on the knowledge of the modulation alphabet is used to resolve a phase ambiguity in the multiuser channel. Through numerical evaluations, we validate the efficacy of the proposed method in effectively resolving preamble collisions.

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.

This paper presents a new high-rate data encoder structure for Wake-Up Signals (WUS) in wireless networks that serve terminals equipped with low-power wake-up receivers. The encoder yields better missed detection performance compared to uncoded transmissions and prior solutions, whereas its contained complexity copes with low-power receivers' typcal limitations in memory size and processing capability. The encoder uses a maximum distance separable (MDS) or almost-MDS code in order to guarantee low false alarm probability. The terminal identity is encoded by a novel low-complexity method based on associated polynomials (AP) over Galois fields. A randomized rate-matching block selects a given number of consecutive symbols at a random position from the MDS codeword and encodes them by an error correction code. The obtained codeword is modulated and transmitted. Randomized rate-matching provides common randomness be-tween transmitter and receivers, which is needed in order to obtain vanishing false alarm probability according to the Identification via Channels framework [1]. The random number generators (RNG) within rate matching are initialized with a same seed at the transmitter and receivers. Thus, unlike prior solutions, sending transmitter-generated random indices within the WUS is no longer required. This allows usage of stronger error correction codes compared to prior solutions, thereby producing SNR gains larger than 4 dB in terms of missed detection compared to uncoded transmissions, and orders of magnitude false-alarm probability gains. Moreover, the RNG seed is kept confidential among network nodes, thereby preventing generation of counterfeit WUSs by potential attackers.

We investigate an unsourced coded slotted random access (RA) protocol which combines physical and MAC layer approaches. In contrast to the literature, we consider MAC-layer slotting which carries information. We distinguish three categories w.r.t. the amount of information carried by the slotting principle; non/partial/full information carrying setups. We model physical layer performance in a slot with a pilot sequence transmission selected based on information, combined with a finite block length code. For MAC-layer non/partial/full information carrying slotting, we use interference-free (IF) constant weight codes with different numbers of packet repetitions, and compare averaged per user block error rate performance with grant-free 5G NR 2-step RA. We observe that the full information carrying setup provides the best results for all slot repetition schemes, and in addition such schemes have the potential to significantly outperform 5G-NR RA. Also, partial information carrying schemes can provide a large portion of the gain over non-information carrying schemes for the same receiver complexity.

Cellular communication systems are currently evolving to provide non-terrestrial networks (NTNs) connectivity. However, due to large link path loss and realistic antenna capabilities of commercial smartphones, direct access to low Earth orbiting (LEO) satellites can so far only provide very small data rates. In this paper, we investigate the potential in using multi-dimensional constellations (MDC) for improving NTN connectivity. MDC allows non-coherent detection over coherent fading blocks, which can reduce the pilot overhead for channel estimation and remove sensitivity to channel estimation quality in low signal-to-noise ratio links. Our simulation results show that the considered MDC scheme can almost double the data rate compared to a NR-type scheme in the considered coverage-limited LEO scenario of small transport block transmission under NTN line-of-sight channel.

A wake-up signal (WUS) can be transmitted from the base station to the user equipment (UE) in order to power-on a UE that was put in sleep mode. The UE may have a dedicated radio receiver for the WUS, which is highly optimized for power efficient operation and the WUS preferably uses a simple waveform which can be non-coherently detected. Thus, multiplexing of WUSs on the same time-frequency resource cannot be done with classical code division multiplexing (CDM). We propose a new multiplexing method of WUSs which is performed prior to the modulator, which allows to use a non-coherently detected waveform. This can be formulated as an encoding problem and we discuss constructions of such multiplexing codes. In particular, we address methods with low complexity to demultiplex the WUSs. The results show that the proposed multiplexing scheme could outperform time division multiplexing (TDM).

This paper introduces a novel physical-layer method labelled as Multi-Modal Concurrent Transmission (MMCT) for efficient transmission of multiple data streams with different reliability-latency performance requirements. The MMCT arranges data from multiple streams within a same physical-layer transport block wherein stream-specific modulation and coding scheme (MCS) selection is combined with joint mapping of modulated codewords to Multiple-Input Multiple-Output spatial layers and frequency resources. Mapping to spatial-frequency resources with higher Signal-to-Noise Ratios (SNRs) provides the required performance boost for the more demanding streams. In tactile internet applications, wherein haptic feedback/actuation and audiovideo streams flow in parallel, the method provides significant SNR and spectral efficiency enhancements compared to conventional 3GPP New Radio (NR) transmission methods.

Constant amplitude zero autocorrelation (CAZAC) sequences have modulus one and ideal periodic autocorrelation function. Such sequences are used in cellular radio communications systems, e.g., for reference signals, synchronization signals and random access preambles. We propose a new family CAZAC sequences, which is constructed by interleaving a Zadoff-Chu sequence by a quadratic permutation polynomial (QPP), or by a permutation polynomial whose inverse is a QPP. It is demonstrated that a set of orthogonal interleaved Zadoff-Chu sequences can be constructed by proper choice of QPPs.

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.

Deep neural network (DNN)-assisted channel coding designs, such as low-complexity neural decoders for existing codes, or end-to-end neural-network-based auto-encoder designs are gaining interest recently due to their improved performance and flexibility; particularly for communication scenarios in which high-performing structured code designs do not exist. Communication in the presence of feedback is one such communication scenario, and practical code design for feedback channels has remained an open challenge in coding theory for many decades. Recently, DNN-based designs have shown impressive results in exploiting feedback. In particular, generalized block attention feedback (GBAF) codes, which utilizes the popular transformer architecture, achieved significant improvement in terms of the block error rate (BLER) performance. However, previous works have focused mainly on passive feedback, where the transmitter observes a noisy version of the signal at the receiver. In this work, we show that GBAF codes can also be used for channels with active feedback. We implement a pair of transformer architectures, at the transmitter and the receiver, which interact with each other sequentially, and achieve a new state-of-the-art BLER performance, especially in the low SNR regime.

Motivated by using non-coherent transmission for coverage enhancement of 5G uplink control channel, this paper proposes a symbol-likelihood based successive cancellation list (SCL) polar decoder that takes into account the impact of constellation modulation. The conventional SCL polar decoding is based on likelihoods of individual coded bits, implicitly assuming independence among them. To circumvent the issue that in practice bit-dependency may occur for bits transmitted in the same constellation symbol, an interleaver is typically inserted before bit-to-symbol mapping. However, interleaving cannot be effective if the transmission is made of only few symbols, as in short packet non-coherent communications typically using high-order multi-dimensional constellations. The proposed decoder is shown to effectively solve this problem and improves the block error rate in a short packet regime, without needs for changing the encoder. Moreover, this symbol-based decoding can still be efficiently performed in a recursive manner by using a data flow graph with butterfly structure as in conventional polar decoding.

Ultra-reliable short-packet communication is a major challenge in future wireless networks with critical applications. To achieve ultra-reliable communications beyond 99.999%, this paper envisions a new interaction-based communication paradigm that exploits feedback from the receiver. We present AttentionCode, a new class of feedback codes leveraging deep learning (DL) technologies. The underpinnings of AttentionCode are three architectural innovations: AttentionNet, input restructuring, and adaptation to fading channels, accompanied by several training methods, including large-batch training, distributed learning, look-ahead optimizer, training-test signal-to-noise ratio (SNR) mismatch, and curriculum learning. The training methods can potentially be generalized to other wireless communication applications with machine learning. Numerical experiments verify that AttentionCode establishes a new state of the art among all DL-based feedback codes in both additive white Gaussian noise (AWGN) channels and fading channels. In AWGN channels with noiseless feedback, for example, AttentionCode achieves a block error rate (BLER) of 10−7 when the forward channel SNR is 0 dB for a block size of 50 bits, demonstrating the potential of AttentionCode to provide ultra-reliable short-packet communications.

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.

We propose a waveform wherein orthogonal basis functions are constructed from cyclically shifted versions of a zero autocorrelation (ZAC) sequence. It is shown that the waveform can equivalently be represented as filtered discrete Fourier transform spread OFDM (DFT-s-OFDM). Chirp sequences are one type of ZAC sequence, however, they have high implementation complexity, and we utilize simpler biphase ZAC sequences instead. The results show that lower error rates on time-frequency selective channels are obtained than for orthogonal frequency division multiplexing (OFDM) and DFT-s-OFDM. We derive correlation properties and find that the waveform is also suitable as a synchronization signal, since modulation symbols can be chosen to obtain an ideal periodic autocorrelation function (PACF) and low peak-to-average-power ratio (PAPR).

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.

We introduce a new family of error correction codes based on sparse superposition called Quasi- Orthogonal} Sparse Superposition Codes (QO-SSC). The core of QO-SSC is a special structure of the SSC projection matrix which is obtained by concatenation of orthogonal submatrices. Concrete examples of QO-SCC constructions based on Zadoff- Chu sequences and Kerdock bent sequences are provided. A low-complexity iterative successive interference cancellation algorithm is proposed for QO-SSC decoding. Performance evaluations show that QO-SSC is an efficient solution for short- packet transmission at low signal-to-noise ratios, as it achieves lower block error rate than conventional coded modulation schemes, e.g., QPSK- modulated polar codes. As a further advantage, QO-SSC features a low PAPR when transmitted using OFDM waveforms.

We propose a novel Simultaneous Wireless Information and Power Transmission (SWIPT) scheme to enable a compatible multiplexing of energy and information based on the frequency that can be used with the state-of-art transceivers. In the proposed scheme, the transmitter superimposes a Direct-Current (DC) signal on Orthogonal Frequency-Division Multiplexing (OFDM) Radio Frequency (RF) signal to generate OFDM-DC signal for SWIPT where the OFDM part is used for information transmission and the DC signal is used for energy transfer. The power level of the DC signal is configured by a controller at the transmitter side. The corresponding receiver is constructed with direct-conversion-receiver front-end such that the DC signal is extracted using a low-pass filter whose bandwidth is configured based on the subcarrier spacing of the OFDM waveform and then fed to a voltage-to-current converter to generate current to charge a battery for energy storage. The OFDM signal without DC power signal is then fed to Analog-to-Digital (A/D) converter for information decoding. The numerical and simulation evaluations provide encouraging evidence in the favor of the proposed OFDM-DC scheme.

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.

A general construction of a particular class of zero correlation zone sequences is proposed. The general construction produces the sets of so-called interference-free zero autocorrelation zone (IF-ZAZ) sequences, where any two sequences from a set have all-zero periodic cross correlation, while each sequence has periodic autocorrelation equal to zero in multiple zones of non-zero delays. The length D of each such ZAZ has the maximum possible value D = t - 1 for given sequence length N = tm and for the given number of sequences in the set M = m. As an important special case of the general construction, we present the construction of generalized chirp-like IF-ZAZ sequences that allow particularly simple implementation of the corresponding banks of matched filters.

This paper investigates the application of N-continuous spectral projection precoding design to single-carrier frequency-division multiple access (SC-FDMA). It first considers a general orthogonal projection-based precoded system with an improved iterative receiver and analyzes its ultimate performance in an additive white Gaussian noise channel, both in terms of achievable throughput and symbol-error rates. For N-continuous SC-FDMA, the distribution of the symbol errors is very much asymmetric; a few base pulses carry the lion share of the self-induced interference, resulting in a zero throughput. We show that an optimized transmission and reception scheme based on a polarized use of the base pulses can satisfactorily deal with this asymmetry, and the end-to-end throughput can be recovered to be close to optimal. Applying a similar scheme to N-continuous OFDM enables also an improved performance in the high-SNR regime, where the interference effect strikes the most.

Superposed transmission on the broadcast channel delivers multiple private messages simultaneously to the intended users. Superposed transmission is employed in non-orthogonal multiple access to increase the aggregate throughput and connectivity of wireless cellular systems. Rate-adaptive constellation Expansion Multiple Access (REMA, a.k.a. RA-CEMA) is a non-orthogonal multiple access scheme which exhibits performance similar to the conventional superposed transmission schemes for transmission on the degraded broadcast channel, while requiring less complex signal processing and scheduling algorithms. This paper solves the problem of user scheduling and rate allocation for REMA. We pose the problem as a weighted sum-rate optimization and develop provably optimal algorithms for user selection and rate allocation with REMA broadcast-channel transmission. System-level evaluations show that our schemes outperform an LTE-A compliant orthogonal multiple access system and exhibit similar or better performance compared to other known non-orthogonal multiple access schemes.

A new non-orthogonal multiple access scheme performing simultaneous transmission to multiple users characterized by different signal-to-noise ratios is proposed. Different users are multiplexed by storing their codewords into a multiplexing matrix according to properly designed patterns and then mapping the columns of the matrix onto the symbols of a higher-order constellation. At the receiver, an interference cancellation algorithm is employed in order to achieve a higher spectral efficiency than orthogonal user multiplexing. Rate-Adaptive Constellation Expansion Multiple Access (RA-CEMA) is an alternative to conventional superposition coding as a solution for transmission on the degraded broadcast channel. It combines the benefits of an increased spectral efficiency with the advantages of reusing the coding and modulation schemes already used in contemporary communication systems, thereby facilitating its adoption in standards.

We propose an enhanced version of trellis coded multiple access (TCMA), an overloaded multiple access scheme that outperforms the original TCMA in terms of achieved spectral efficiency. Enhanced TCMA (ETCMA) performs simultaneous transmission of multiple data streams intended for users experiencing similar signal-to-noise ratios and can be employed both in the uplink and in the downlink of wireless systems, thus overcoming one of the main limitations of TCMA. Thanks to a new receiver algorithm, ETCMA is capable of delivering a significantly higher spectral efficiency. We show that ETCMA approaches the capacity of the Additive White Gaussian Noise channel for a wide range of signal-to-noise ratios.

Achieving higher aggregate data rates for many simultaneous users is considered as a fundamental challenge for the next generation of wireless systems. With low-density spreading (LDS), one could transmit information by overloading, i.e., using more spreading sequences than chips with reasonable implementation complexity. In this paper, we propose an improvement to the conventional LDS technique that consists in introducing a bit interleaver in the transmission scheme. Its role is to render the error bursts that appear at the output of the LDS detector into correctable patterns for the channel decoder. Numerical evaluations of the spectral efficiency show SNR improvements of more than 2dB when using convolutional codes in BI-LDS schemes. Slight improvements are also observed when turbo codes are employed.

A quasi-orthogonal (QO) set of sequences is a union of a number of different orthogonal sets of sequences, where all the sequences are of the same length and energy, such that the absolute value of the inner product of any two sequences belonging to the different orthogonal sets is much less than the energy of the sequences. In this paper we present several supersets of QO sequences, each being a union of an existing QO set and a number of new QO sets obtained through the unique transformations of the existing QO set. Three interesting specific QO supersets are considered, based on the QO sets of quadratic polynomial phase sequences transformed through the signature sequences such as: the higher-degree polynomial phase sequences, the Constant Amplitude Zero Autocorrelation (CAZAC) sequences (in particular, the Björck sequences), and m-sequences.

In this paper, a new construction of optimum sets of zero correlation zone (ZCZ) sequences, derived from generalized chirp-like (GCL) sequences, is presented. A special case with reduced alphabet size is also described. In a set of GCL-ZCZ sequences, the length of the zero correlation zoneDhas the maximum possible valueD=t- 1 for a given sequence lengthN=tmand for a given number of sequences in the setM=m. Many values ofNcan be decomposed into multiple products of two positive integers, thus allowing for flexible tradeoff between the length of the ZCZ and the number of sequences in the set. As the set of GCL-ZCZ sequences is obtained by modulating a common ¿carrier¿ sequence with a set of orthogonal modulating sequences, there is a possibility for efficient implementation of the corresponding bank of matched filters.

We present sets of spreading sequences that are specifically designed to suit a belief-propagation multiuser detection structure, recently presented for overloaded system scenarios. On one hand, our sequences are of the low-density type; on the other their distance spectrum properties ensure good performance in AWGN channels. Simulations results for raw and coded bit-error probability indicate that significant performance gain is achieved over random sequences and that the loss compared to the single-user bound can be kept small.

Cell search is the procedure by which a mobile terminal acquires time and frequency synchronization to the network and detects a cell identity. In this paper, we give a non-hierarchical scheme for OFDM systems, where cell-specific signals are concurrently used for synchronization and cell identification. By using time-domain symmetric signals, the symbol timing is accurately found by a reverse differential correlator. Once the timing is established and frequency offsets are estimated, detection of the transmitted synchronization sequence is done non-coherently by means of a differential decoder. The frame timing is obtained by letting different synchronization signals represent elements of cyclically unique codewords over a radio frame. The scheme can convey large amount of cell identities and numerical results show that it is robust to frequency offsets.

The required power back-off in the uplink of the Evolved UTRA cellular system is considered in this paper. It is shown that the discrete prolate spheroidal window is optimum for the reduction of the peak-to-average ratio by spectrum shaping. It is also useful for reducing the cubic metric. Measures for power back-off and results for required average power are presented for different spectrum shaping functions. It is shown that spectrum shaping with the optimum functions reduces the required power back-off with small increase in the required average power for pi /2-shifted BPSK and low to intermediate data rates.

Transmit power rise (TPR) in code-division multiple-access (CDMA) systems can be defined as the ratio of the average transmit power to the average receive power, where the average total channel power attenuation is assumed to be one. The TPR has been practically used in the Universal Mobile Telecommunications System radio network planning for modeling of the joint impact of the fast power control, the propagation channel power attenuations, and the antenna diversity. In this letter, we present a general analytical formula for the calculation of TPR in CDMA systems with fast power control, for an arbitrary multipath power profile, arbitrary numbers of transmit and receive antennas, and arbitrary maximum transmit power.

A general construction for orthogonal sets of quadriphase sequences based on the sequence family A discovered by Sole (1989), Boztas, Hammons, and Kumar (1992) is presented. The sequence family A is equivalent to the S(0) family that belongs to a chain of sequence families S(i),i=0,1,2,..., m with each family in the chain containing the preceding family. Therefore, a number of orthogonal subsets can be generated for an arbitrary family S(m). The algorithm for an efficient implementation of the bank of correlators corresponding to any orthogonal subset of family S(m) is derived as well.

The paper contains an analysis of the basic criteria for the selection of spreading sequences for the multicarrier CDMA (MC-CDMA) systems with spectrum spreading in the frequency domain. It is shown that the time-domain crosscorrelation function between the spreading sequences is not a proper interference measure for the asynchronous MC-CDMA users. Therefore, the spectral correlation function is introduced and, together with the crest factor and the dynamic range of the corresponding multicarrier waveforms, is used for the evaluation of MC-CDMA sequences. Some well-known classes of sequences, such as Walsh, Gold, orthogonal Gold, and Zadoff-Chu sequences, as well as Legandre and Golay complementary sequences, are evaluated with respect to the aforementioned basic criteria. It is also shown that the crest factors of the multicarrier spread spectrum waveforms based on the multilevel Huffman sequences are very close to or even lower than the crest factor of a single sine wave.

A new general class of polyphase sequences with ideal periodic autocorrelation function is presented. The new class of sequences is based on the application of Zadoff-Chu polyphase sequences of length N=sm/sup 2/, where s and m are any positive integers. It is shown that the generalized chirp-like sequences of odd length have the optimum crosscorrelation function under certain conditions. Finally, recently proposed generalized P4 codes are derived as a special case of the generalized chirp-like sequence.>

It is shown that, generally, any binary or polyphase sequence belonging to a pair of complementary sequences can be used to construct the initial phases of tones forming a multitone signal with the crest factor less than or equal to 6 dB. The previously proposed Shapiro-Rudin sequences are representatives of a much larger family of binary Golay complementary sequences. Numerical investigations show that the values of the crest factors obtained by applying complementary sequences (binary or polyphase) are between 5 and 6 dB, regardless of the number of tones.>

For the original article see ibid., vol.COM-35, no.5, p.566-8 (1987). It is pointed out that in the paper by I. Vajda and G. Einarsson the proposed sets of frequency-hopping sequences, that permit the correct resynchronization in FH-MFSK (frequency-hopping multiple-frequency-shift-keyed) multiple-access systems, are only the special case of the Reed-Solomon sets of asynchronous frequency-hopping sequences previously derived. For the case when the number of available frequencies is prime, another class of FH-MFSK sequences with good resynchronization and interference properties is presented.>