This paper presents a technology of sensing hidden vehicles by exploiting multi-path vehicle-to-vehicle (V2V) communication. This overcomes the limitation of existing RADAR technologies that requires line-of-sight (LoS), thereby enabling more intelligent manoeuvre in autonomous driving and improving its safety. The proposed technology relies on transmission of orthogonal waveforms over different antennas at the target (hidden) vehicle. Even without LoS, the resultant received signal enables the sensing vehicle to detect the position, shape, and driving direction of the hidden vehicle by jointly analyzing the geometry (AoA/AoD/propagation distance) of individual propagation path. The accuracy of the proposed technique is validated by realistic simulation including both highway and rural scenarios.

Mobile-edge computation offloading (MECO) off-loads intensive mobile computation to clouds located at the edges of cellular networks. Thereby, MECO is envisioned as a promising technique for prolonging the battery lives and enhancing the computation capacities of mobiles. In this paper, we study resource allocation for a multiuser MECO system based on time-division multiple access (TDMA) and orthogonal frequency-division multiple access (OFDMA). First, for the TDMA MECO system with infinite or finite cloud computation capacity, the optimal resource allocation is formulated as a convex optimization problem for minimizing the weighted sum mobile energy consumption under the constraint on computation latency. The optimal policy is proved to have a threshold-based structure with respect to a derived offloading priority function, which yields priorities for users according to their channel gains and local computing energy consumption. As a result, users with priorities above and below a given threshold perform complete and minimum offloading, respectively. Moreover, for the cloud with finite capacity, a sub-optimal resource-allocation algorithm is proposed to reduce the computation complexity for computing the threshold. Next, we consider the OFDMA MECO system, for which the optimal resource allocation is formulated as a mixed-integer problem. To solve this challenging problem and characterize its policy structure, a low-complexity sub-optimal algorithm is proposed by transforming the OFDMA problem to its TDMA counterpart. The corresponding resource allocation is derived by defining an average offloading priority function and shown to have close-to-optimal performance in simulation.

A bit-error-rate (BER)-based physical layer security approach is proposed for the finite blocklengths. For secure communication in the sense of high BER, the information-theoretic strong converse is combined with cryptographic error amplification achieved by the substitution permutation networks based on the confusion and diffusion. For the discrete memoryless channels (DMCs), an analytical framework is provided showing the tradeoffs among the finite blocklength, the maximum/minimum possible transmission rates, and the BER requirements for the legitimate receiver and the eavesdropper. In addition, the security gap is analytically studied for the Gaussian channels and the concept is extended to other DMCs including the binary symmetric channels and binary erasure channels.

Recently, study on designing a new metric to express quality of experience (QoE) has attracted attention since user satisfaction may be different according to the types of served traffic. The utility function for various traffic has been studied for many years and most of the previous work focused on the utility functions with respect to a single performance metric such as throughput. However, multiple performance metrics may affect user satisfaction according to user properties or situations. One of critical factors that affect the sensitivity of user satisfaction is the remaining battery energy. In this paper, we investigate the characteristics of the user satisfaction with respect to throughput and energy efficiency considering the remaining battery energy. Based on the characteristics, we design a multi-variable QoE function based on the unified utility, especially, considering user's remaining battery energy and verify the feasibility of the proposed multi-variable QoE function through numerical results.

Deployment of small cells is one of the most efficient solutions to improve the energy efficiency in mobile communication networks. However, small cell topology has a disadvantage such as frequent handovers of mobile user equipments (UEs). To solve this handover problem for small-cell users in a HetNet environment, we propose a novel handover scheme utilizing a cooperation-based cell clustering scheme for reducing handover overhead in core network (CN) and also signaling overhead among small cells. When a UE in active mode moves randomly, we can significantly reduce the handover ratio through the proposed scheme, compared with that of the conventional schemes. In particular, if the UE speed is 3 km/h, this ratio is approximately 0.07.

In this letter we propose per antenna superposition coding (PASC) by which partial information can be relayed instead of full information, to exploit the higher capacity of source-relay-destination link. Here, the PASC is designed across antennas, producing basic layer and superposed layer for each data stream per antenna. It is shown that an overall data rate of partial information relaying with PASC can be increased beyond that offered by full information relaying by virtue of fast forwarding of partial information over relatively better link.

This paper proposes an adaptive multi-node incremental relaying technique in cooperative communications with amplify-and-forward (AF) relays. In order to reduce the excessive burden of MRC with all diversity paths at the destination node, the destination node decides if it combines signals over the first N(<; K) time slots/frames or over all of the K times slots, where K is the number of relay nodes. Our analytical and simulation results show that the proposed adaptive multi-node incremental relaying outperforms the conventional MRC in terms of outage probability in AF based cooperative communications since the proposed scheme effectively reduces the spectral efficiency loss. Our asymptotic analysis also shows that the proposed adaptive multi-node incremental relaying achieves full diversity order K + 1.

This paper proposes a novel generalized selection combining (GSC)/maximal ratio combining(MRC) switching technique based on error detection in cooperative communications with amplify-and-forward (AF) relays. In order to reduce the excessive burden of MRC with all diversity paths at the destination node, the destination node decides if it performs GSC with order N(< K) or MRC with order K + 1 based on the error detection, where K is the number of relay nodes. Our analytical and simulation results show that the proposed GSC/MRC switching outperforms the conventional MRC in terms of outage probability in AF based cooperative communications since the proposed scheme effectively reduces the spectral efficiency loss with the help of error detection codes.

This paper revisits an optimal rate and power allocation problem to maximize throughput in uplink CDMA single-cell packet data communications. First, we show that the widely-accepted belief that an optimally selected rate always keeps a constant value of the resulting bit energy to the interference plus noise power spectral density ratio is not true in most practical CDMA packet transmission environments, where the packet size varies in proportion to the rate. Then, we derive the rate-dependent optimal bit energy-to-interference-noise power spectral density ratio, based on which we convert the original joint optimization problem of rate and power to an equivalent but simple power allocation problem. Finally, we derive an optimal power allocation strategy by applying the convex optimization theory. Through two instructive examples, we show that the optimality of the well-known bang bang power control, that is, each user (except at most one user) should either transmit his data at the maximum allowed power level or at the minimum required power level meeting the SINR requirement in order to maximize the system throughput, may or may not be true depending on the incorporated channel coding scheme.

In this paper we introduce selective virtual antenna permutation (S-VAP) for layered OFDM-MIMO transmission in downlink cellular environments. In the S-VAP scheme, the base station spatially permutes multiple independently encoded layers and then transmits the permuted layers over selected virtual antennas. The mobile station employs a successive interference cancellation (SIC) based receiver to maximize the spectral efficiency. The layer permutation enables a significant reduction of channel quality feedback information necessary to adjust the data rate of each layer. Transmission over selected virtual antennas instead of physical antennas enables efficient power amplifier utilization and thus brings out a quantized spatial water-filling gain.

This paper proposes an enhanced chip-level linear space-time equalizer for multiple-input-multiple-output (MIMO) multi-code CDMA systems. In the MIMO multi-code CDMA systems, the reuse of the same spreading codes in different transmit antennas significantly degrades the equalization performance if the space-time equalizer uses a weighting vector that minimizes the mean squared error of the equalizer output chip sequence. As the CDMA despreader concatenated to a space-time equalizer distorts inter-stream interference components differently from multipath interference and background noise components, the traditional chip-level minimum mean squared error (MMSE) weighting vector usually steers in a sub-optimal direction in the signal space. Therefore, we propose a new MMSE weighting vector that takes the despreading effect into account in this paper. Simulation results show a substantial performance improvement through the new weighting vector.

This paper proposes a new RAKE receiver incorporated with a bidirectional iterative intersymbol interference (ISI) canceller in order to reinforce multipath robustness of high-rate direct-sequence spread-spectrum complementary code keying (DSSS/CCK) systems. The proposed RAKE receiver first combines multipath signal components through a channel matched filter (CMF) and removes postcursor-ISI by employing a codeword decision feedback equalizer (DFE). Then, a CCK codeword detector tentatively determines the current CCK codeword symbol and reuses it to subtract precursor-ISI from the previous symbol. Therefore, the ultimate symbol decision is made using the delayed signal with both postcursor-ISI and precursor-ISI cancelled. The detection performance can be more improved through an iterative refinement processing between the postcursor and the precursor components. Simulation results exhibit a significantly improved error rate performance of the proposed receiver compared with that of the legacy RAKE receiver employing only a postcursor DFE. The additional cost for realization of the proposed receiver is one symbol decision delay and reuse complexity of the DFE and the codeword detector.

We first present the traditional decoding approach that employs the common pilot-channel-based maximal ratio combining and the Viterbi or iterative decoding cannot achieve the optimal error-rate performance for downlink direct-sequence code-division multiple-access (CDMA) signals when a fast power control technique is applied together with a convolutional or turbo coding. Then, as an efficient method to realize a nearly optimal decoding, we propose a branch metric power readjustment (BMPR) technique, where the downlink power control command generated by the mobile station is used not only to adjust the base station power in the transmitter side, but also to readjust the decoder input branch metric power in the receiver side. Numerical results show that the BMPR technique applied to the IMT-2000 wideband-CDMA system can improve the transmit power utilization by up to 0.4 dB for the block-error rate of 10/sup -2/.

In this paper, we show that the traditional decoding approach employing the pilot channel based maximal ratio combining and the Viterbi or iterative decoding cannot achieve the optimal error rate performance for downlink DS/CDMA signals when a fast power control technique is applied together with a convolutional or turbo coding. Then, as an efficient method to realize a nearly optimal decoding, we propose a dual power control (DPC) technique, where the downlink power control command generated by the mobile station is used not only to adjust the base station power in the transmitter side but also to readjust the decoder input symbol power in the receiver side. Numerical results show that the DPC technique applied to the IMT-2000 W-CDMA system can improve the signal-to-interference ratio by about 0.4 dB for the block error rate of 10/sup -2/ at the cost of a simple power re-adjustment operation.

We introduce a correlation-aided distributed sample acquisition (CDSA)-based intercell synchronous direct-sequence code-division multiple-access (DS/CDMA) system for enhancing the robustness of the previously proposed distributed sample acquisition (DSA)-based system. The CDSA system incorporates the state symbol correlation process in the existing DSA process to maintain the fast acquisition performance even under very poor channel environment. For its realization, each CDSA-based mobile station stores in its memory a period of the possible state symbol sequences, which are determined by the long-period scrambling PN sequences used in the system and the sampling time parameters for the state samples. In the first stage of the synchronization procedure, the mobile station (MS) attempts to acquire the psuedo noise (PN) sequence by taking the comparison-correction based synchronization approach of the original DSA scheme. However, if it cannot acquire the synchronization until it collects a predetermined number of state symbols (e.g., a period of the state symbol sequence), then the MS determines the PN sequence timing by correlating the received symbol sequence with each shift of the prestored state symbol sequences. Performance analysis and simulation results reveal strong robustness of the CDSA-based system in low-signal-to-noise ratio, fading, and large frequency-offset channels.

We propose a parallel distributed sample acquisition (PDSA) scheme applicable to a direct-sequence code-division multiple-access (DS/CDMA) system employing M-ary signaling for data transmission. While the primitive distributed sample acquisition scheme can be employed only for the binary signaling systems which transmit 1 bit per symbol, the proposed PDSA scheme extends its applicability to the general signaling systems allowing multibit transmission per symbol. The proposed PDSA technique can also be applied to fast acquisition of the scrambling code in multicarrier DS/CDMA cellular systems with a slight modification of the transceiver circuitry.

The paper presents a new spread spectrum communication system called orthonormal code diversity detection (OCDD)/CDMA system based on the novel concept of orthonormal-basis diversity which is a generalization of the existing spread spectrum diversity concepts such as path diversity and frequency diversity. The OCDD/CDMA system is similar to the conventional DS/CDMA system in the transmitter structure, but is different in the receiver structure as it employs the extended orthonormal basis-function set which is the union of the Walsh basis-functions multiplied by the PN sequences and, optionally, their delayed replicas. The received signal is matched to the extended basis functions, and the matched signal components are combined together after individual channel compensation. The proposed OCDD/CDMA system exhibits the bit error performance which is much improved over the conventional DS/CDMA system using maximal ratio combing. In addition, it is robust to the chip timing error, which becomes more crucial in the future DS/CDMA systems having a higher data rate and smaller chip interval. From the simulation results, we confirm that the OCDD/CDMA system is a unique spread spectrum communication technique that can effectively increase the diversity utilization in the slowly fading channel, overcoming the inherent problems in the DS/CDMA and OFDM/CDMA systems.

We present DPSK-based distributed sample acquisition (D/sup 2/SA) as a novel variant of the distributed sample acquisition family for application to the M-ary phase-shift keying signaling direct-sequence code-division multiple-access systems. The D/sup 2/SA employs differentially coherent phase-shift keying (DPSK) to convey the shift register generator state samples and the prerotation of the data constellation to realize the coherent demodulation of the data stream. The use of DPSK instead of orthogonal modulation as the means of the state sample conveyance improves the system performance in terms of both system complexity and acquisition time.

We introduce a fast fell-search scheme based on the distributed sample acquisition (DSA) technique for inter-cell asynchronous DS/CDMA systems. The proposed DSA scheme enables the long-code acquisition extremely fast even without employing any passive matched filter which used to dominate synchronization circuit complexity in asynchronous DS/CDMA systems. In the DSA-based asynchronous DS/CDMA system, each base station spreads its DQPSK-modulated long-code generator information with an assigned short-period igniter sequence, and broadcasts it as a common pilot signal. A mobile station first identifies and acquires the igniter sequence of the cell group currently located, then detects the conveyed long-code generator information by despreading the acquired igniter sequence, thereby identifying and synchronizing the long-code of the current cell. The mean acquisition time of this proposed DSA-based inter-cell asynchronous DS/CDMA system, evaluated under the assumption that each of 512 cell-specific long-codes is a 10-ms segment (38400-chips for the chip rates of 3.84 Mchips/s) of complex Gold codes of period 2/sup 18/-1 and the igniter sequence (or, group code) set is composed of 7 complex orthogonal Gold codes of period 256, turned out even shorter than that of the inter-cell synchronous DS/CDMA systems employing the conventional serial search method. Furthermore, simulation results showed that the DSA scheme employing a passive matched filter is much superior in terms of acquisition time and robustness, to the 3GPP W-CDMA synchronization scheme having comparable complexity.

We propose a new acquisition scheme called distributed sample acquisition (DSA) which is applicable to the direct-sequence code-division multiple-access (DS/CDMA) system with a long-period pseudonoise (PN) sequence. The proposed scheme lays its foundations on an auxiliary PN sequence called the igniter sequence, which has relatively short period, and the distributed sample scrambling (DSS) technique previously developed for the asynchronous transfer mode cell transmission. In the DSA scheme, acquisition is done in three steps. First, the igniter sequence is synchronized, which normally takes a very short time due to its short period. Second, the state samples of the long-period PN sequence generator in the transmitter, which are conveyed to the receiver over the igniter sequence stream, are determined out of the synchronized igniter sequence. Third, the long-period PN sequence is synchronized by applying the state samples to the DSS receiver. Since the operation of each step takes a very short time, the overall acquisition is done very quickly. We analyze the acquisition time performance of the proposed scheme by taking the transform domain approach, confirming that the resulting mean acquisition time is dramatically reduced. If compared with the existing serial-search scheme, the DSA scheme can perform acquisition about 100 times faster when the period of the PN sequence is 2/sup 15/-1. None the less, the additional circuit complexity for its implementation is very small.

We analyze the acquisition time performance of the distributed sample acquisition (DSA) scheme proposed for a fast DS/CDMA signal acquisition. To analyze the composite acquisition mechanism, we first define several acquisition-related probability parameters which can describe all the essential events in the DSA synchronization, along with the basic states that constitute the eventual DSA state transition diagram. Then, we construct the state transition diagram employing these basic states and the moment generating functions which are entirely based on the above defined probability parameters. Applying this state transition diagram and determining the acquisition-related parameters, we finally analyze the mean acquisition time performance of the DSA.

This paper introduces a new acquisition scheme called distributed sample acquisition (DSA), which is applicable to the DS/CDMA system with a long-period PN sequence. The DSA scheme employs two new concepts, igniter sequence and distributed samples, for signal acquisition. The igniter sequence is a short-period sequence that conveys the main-sequence samples of the transmitter to receiver in a distributed manner, which are thus called distributed samples. In synchronizing the igniter sequence, we employ normal serial search schemes, but for synchronization of the main long-period PN sequence we employ the novel distributed sample scrambling (DSS) technique. The resulting mean acquisition time of the DSA scheme is dramatically reduced for the long period PN sequence, and the additional circuit complexity for its implementation is very small.