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.

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).

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.

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.

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.

LTE-Advanced supports carrier aggregation which implies that ACK/NACK information bits for multiple downlink carriers are fed back in the uplink. One method for HARQ feedback with multiple ACK/NACK bits is channel selection, wherein ACK/NACK information is encoded by the joint selection of a channel (transmit sequence) and a QPSK symbol. We give a signal design for mapping ACK/NACK information to the channels and modulation symbols, in order to minimize and equalize the ACK-to-NACK and NACK-to-ACK error probabilities. It is shown how the performance depends on the set of channels assigned to a given ACK/NACK bit.

This contribution addresses the potential of N-continuous OFDM signals in systems where the receiver is unaware of the transmitter precoder operation. First, we present a memoryless precoder rendering N-continuous signals. Second, we evaluate the effect on the magnitude of the emitted signal's error-vector. Third, we present three ad hoc precoders designed under a hard constraint on the allowed EVM still significantly suppressing out-of-band power.

Multi-access networks integrate a number of radio accesses (RAs) over which a data flow may be transmitted. Considering the possibility of multi-radio transmit diversity (MRTD), where a given flow may be assigned multiple RAs either in parallel or in a switched mode, we investigate mechanisms for joint RA selection and scheduling of data flows onto the selected RAs. We introduce the active set concept for multiaccess networks, consisting of a subset of the available RAs that are chosen by a user for potential handling of its data flow and establish the latitude for access selection. The performance impact of distinct access selection schemes is assessed in multiaccess networks, considering different scenarios in terms of the degree of non cositing, the traffic load and the number of available RAs. Among the key results, we demonstrate that a significant degree of non cositing is beneficial and that the use of MRTD is fruitful in pursuing performance targets of operational relevance.

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.

Motivated by the "beyond 3g" vision of radio access network integration and coordinated radio resource management, a purely analytical performance assessment is presented for a single access point integrating multiple radio accesses. Principal focus is placed on the evaluation of multi-user diversity, multi-access diversity and trunking gains. Scenarios with persistent and non-persistent data flows are investigated, concentrating on throughput and transfer time performance, respectively. A number of numerical experiments are included in order to quantify the relative contribution of the distinguished aspects to the performance gain. These experiments indicate that the exploitation of multi-user diversity with a channel-aware access selection scheme attains the most significant gains, while also the trunking gain that is due to an above-proportional performance enhancement when aggregating system-specific capacities, is noted to be significant. The assignment of multiple accesses to a given flow is demonstrated to have limited potential.

The ambient networks concept targets forthcoming dynamic communication environments, characterized by the presence of a multitude of different wireless devices, radio access technologies, network operators and business actors, which can form instant inter-network agreements with each other. Multi-radio resource management (MRRM) mechanisms, coordinating several radio accesses, fulfill a key role for providing wireless services with improved resource efficiency, coverage and service quality. This paper presents an MRRM concept for Ambient Networks, describes the principal MRRM functions and discusses design criteria.

The current focus on innovative spectrum policies and efficient wireless bandwidth utilization has motivated research on methods for dynamic spectrum access. By letting systems share the spectrum, trunking gains and better utilization of the bandwidth is predicted. From a technical point of view, the paradigm shift to open frequency bands implies a need to investigate and verify resulting capacity gains. In this paper, we give a general method for evaluating system capacity subject to outage probability constraints over fading channels, in an unlicensed environment with uncoordinated systems. The channel fading effects include attenuation, shadowing and multipath propagation and we end up with expressions, solved by numerical integration. The spectrum sharing is here performed by means of autonomous dynamic channel allocation (DCA), and we compare several DCA methods, e.g., maximum SIR and random DCA.

This paper addresses dynamic resource allocation (DRA) for the downlink of a SDMA broadband wireless packet network with multiple access ports and adaptive antennas. The main issue for distributed DRA is how to manage the intercell interference, which is very difficult to be handled in an uncoordinated environment, due to packet access and downlink beamforming. Here, we investigate the performance and the feasibility of some distributed DRA strategies to gain insight on the impact of the lack of coordination among cells. We propose to estimate the intercell interference on the basis of cell load and worst case (taking into account adaptive antennas) measured interference and implement some greedy strategies suitable for a distributed implementation. We show that the gap between random allocation (previously proposed for distributed packet allocation) and a centralized algorithm can be significantly reduced, although the implementation of an efficient distributed power control still appears a hard task.

The problem of scheduling delay insensitive data over a direct sequence code-division multiple-access downlink fading channel is considered. This work considers the case where only one user at a time is allowed to transmit. As the channels can be considered to vary asynchronously among the users, multiuser diversity gains can be obtained by exploiting channel adaptive scheduling. For this, schedulers of different adaptation rate are suggested and compared. In particular, the authors analyze a simple fast scheduler that schedules a user to transmit when its channel is good relative to its mean. This scheduler is resource fair in the sense it can provide the users with the same asymptotic channel access. They show that the achievable scheduling gain compared to round robin is equal to the gain of a selection diversity scheme. The scheduling gain is determined, both on closed-form and by numerical integration, for several scenarios, including multicellular systems and the effect of time delayed channel estimates. The results show that the scheduling gain is larger for channels with low average quality.

The quality of service in direct-sequence code-division multiple access (DS-CDMA) can be controlled by a suitable selection of processing gain and transmission powers. In this paper, distributed control of rate and power for best effort data services is considered. In particular, we elaborate on the problem of how to control the transmission rates for maximizing system throughput while simultaneously minimizing the transmission powers. We assume a practical scenario, where every user has a finite set of discrete transmission rates and propose a simple heuristic rate allocation scheme, greedy rate packing (GRP), applicable in both up- and downlink. The scheme can be interpreted as a practical form of water-filling, in the sense that high transmission rates are allocated to users having high link gains and low interference. We show that under certain conditions, GRP will give maximum throughput and that it can be extended to guarantee a minimum data rate while maximizing network excess capacity. We suggest and analyze a distributed power control algorithm to control the intercell interference when GRP is applied to a multicellular system. Numerical results show that the proposed transmission scheme can significantly decrease the power levels while maintaining high throughput.

Forthcoming wideband wireless systems are supposed to support services with loose delay requirements, which allows for scheduling of data. In this work we investigate fast transmission scheduling for downlink CDMA over a Rayleigh fading channel. For a logarithmic relation between the channel quality and the effective transmission rate, merely scheduling one user at a time may not result in maximum channel utilization. Therefore, we analyze the benefits of scheduling several users at a time with a suggested scheduler, containing regular CDMA as a special case. We consider a resource fair scheduler with the objective to asymptotically allocate the same amount of energy to all users. We derive the scheduling gain on closed-form and determine its limit values for both high and low average channel quality. The results show that the better the average channel quality becomes, the more users should be allowed to transmit simultaneously.

In this work, a linear DS-CDMA receiver utilizing soft feedback interference cancellation is analyzed. To be able to meet diverse QoS requirements, we introduce a power control scheme that takes into account multi-QoS objectives, as well as the impact of imperfect interference cancellation. Our results are general and provide a framework for capacity comparison for many proposed linear successive cancellation receiver models. Several receiver modifications are included, partial interference cancellation: when only part of the signal is canceled, and limited cancellation; when not every signal is canceled. We derive the minimum power solution, from which the resulting receiver capacity can be fully characterized. The results show that there are large gains in user capacity from interference cancellation when the Eb/Io requirements are high. However, regardless of the required targets, we find that the maximum capacity is always achieved through partial successive interference cancellation. It is also found that worse performance than conventional single-user detection can occur.

Abstract Successive interference cancellation techniques have the potential to reduce the interference and therefore increase the capacity of cellular radio systems. In this work, we analyze a linear DS‐CDMA receiver utilizing soft feedback interference cancellation. To be able to meet diverse QoS requirements, we introduce a power control scheme that takes into account heterogeneous service levels as well as the impact of imperfect interference cancellation. We address the capacity resulting from this receiver and give its user capacity region on closed‐form. We show that our results are general and provide a framework for capacity comparison for many proposed linear successive cancellation receiver models. Several receiver modifications are included, partial interference cancellation; when only part of the signal is canceled, and limited cancellation; when not every signal is canceled. We derive the minimum power solution of a single‐cell, from which convergent multicellular distributed power control algorithms that iteratively update the powers are suggested. The numerical results show that there are large gains in user capacity from interference cancellation when theEb/I0requirements are high. However, regardless of the required targets the maximum capacity is always achieved through partial successive interference cancellation. It is also found that the power levels are sensitive to the cancellation efficiency and worse performance than single‐user detection can occur. Copyright © 2003 John Wiley & Sons, Ltd.

We investigate a multi-rate receiver utilizing soft feedback successive interference cancellation. To be able to meet the QoS requirements for each user, the multiuser detection is done in conjunction with power control. For this, we introduce a power control scheme that takes into account the respective QoS requirements and the impact of imperfect interference cancellation. We derive the minimum power solution, from which distributed iterative power control algorithms are suggested. It is found that the rate of convergence of the power control can be accelerated if the cancellation efficiency parameter can be directly incorporated into the power update. We also address the capacity resulting from this receiver in terms of the notion of effective bandwidth.

We consider joint rate and power control in a multi-cellular CDMA system utilizing variable processing gain. We investigate the problem of optimum power allocation for sharing the capacity in a fair way in the whole network. For this, we suggest a general distributed power control algorithm which directs the powers so that a uniform throughput is obtained among the users. We show that the powers converge towards the optimal solution at a geometric rate and how the maximum achievable throughput can be estimated during the power control.

The performance of DS-CDMA systems depends on the success in managing interference arising from both intercell and intracell transmissions. Interference management in terms of power control for real time data services like voice has been widely studied and shown to be a crucial component for the functionality of such systems. In this work we consider the problem of supporting downlink nonreal time data services, where in addition to power control, there is also the possibility of controlling the interference by means of transmission scheduling. One such decentralized schedule is to use time division so that users transmit in a one-by-one fashion within each cell. We show that this has merits in terms of saving energy and increasing system capacity. We combine this form of intracell scheduling with a suggested distributed power control algorithm for the intercell interference management. We address its rate of convergence and show that the algorithm converges to a power allocation that supports the nonreal time data users, using the minimum required power while meeting requirements on average data rate. Numerical results indicate a big potential of increased capacity and that a significant amount of energy can be saved with the proposed transmission scheme.