Distributed MAC and rate adaptation for ultrasonically networked implantable sensors

In this paper, we investigate a novel beam direction-based modulation transmit scheme for millimeter-wave (mmWave) communication systems equipped with distributed antennas, and propose an enhanced space-domain index modulation (ESDIM) scheme, in which the number of beamforming directions (BDs) for transmitting information bits can be one or two. The ESDIM system jointly utilizes the combination of the index of BDs and signal constellations to transmit information bits, in which one or two beam directions are considered. In addition, we propose power allocation (PA) aided schemes for ESDIM to further improve the system reliability by reducing the system symbol error rate (SER), where three constraints to the transmit power for beamforming are investigated. To be specific, a total transmit power constraint (TTPC) and two per-beamforming power constraints (PBPC) are considered. We first propose a suboptimal PA algorithm for the TTPC-PA aided ESDIM scheme using a powerful solver based on advanced algebra theories, which only considers the PA aspects for a given selected beamforming pair. Then, we extend the TTPC-PA aided scheme to the average per-beamforming power constraint (APBPC)-PA aided scheme and the strict per-beamforming power constraint (SPBPC)-PA aided scheme. Simulation results show that the proposed schemes improve the system SER performance compared to other existing counterparts.

Sparse vector coding (SVC) is a promising short-packet transmission method for ultra reliable low latency communication (URLLC) in next generation communication systems. In this paper, a dual-mapping SVC (DM-SVC) based short packet transmission scheme is proposed to further enhance the transmission performance of SVC. The core idea behind the proposed scheme lies in mapping the transmitted information bits onto sparse vectors via block and single-element sparse mappings. The block sparse mapping pattern is able to concentrate the transmit power in a small number of non-zero blocks thus improving the decoding accuracy, while the single-element sparse mapping pattern ensures that the code length does not increase dramatically with the number of transmitted information bits. At the receiver, a two-stage decoding algorithm is proposed to sequentially identify non-zero block indexes and single-element non-zero indexes. Extensive simulation results verify that proposed DM-SVC scheme outperforms the existing SVC schemes in terms of block error rate and spectral efficiency.

The present paper gives an overview of multiple access techniques proposed for the uplink in future wireless communication systems. This paper provides the comparison between Orthogonal Frequency Division Multiple Access (OFDMA) and Single-carrier frequency division multiple access (SC-FDMA) techniques. A survey of Uplink Multiple Access Techniques in LTE Mobile Communication System, their basic features and various issues related to this have been introduced in this paper.

Health monitoring using biomedical sensors has witnessed significant attention in recent past due to the evolution of a new research area in sensor network known as Wireless Body Area Networks (WBANs). In WBANs, a number of implantable, wearable, and off-body biomedical sensors are utilized to monitor various vital signs of patient’s body for early detection, and medication of grave diseases. In literature, a number of Medium Access Control (MAC) protocols for WBANs have been suggested for addressing the unique challenges related to reliability, delay, collision and energy in the new research area. The design of MAC protocols is based on multiple access techniques. Understanding the basis of MAC protocol designs for identifying their design objectives in broader perspective, is a quite challenging task. In this context, this paper qualitatively reviews MAC protocols for WBANs. Firstly, 802.15.4 and 802.15.6 based MAC Superframe structures are investigated focusing on design objectives. Secondly, different multiple access techniques such as TDMA, CSMA/CA, Slotted Aloha and Hybrid are explored in terms of design goals. Thirdly, a two-layered taxonomy is presented for MAC protocols. First layer classification is based on multiple access techniques, whereas second layer classification is based on design objectives and characteristics of MAC protocols. Critical and qualitative analysis is carried out for each considered MAC protocol. Comparative study of different MAC protocols is also performed. Finally, some open research challenges in the area are identified with initial research directions.

High intensity focused ultrasound (HIFU) therapy has become a new way in the treatment of tumors due to its noninvasive advantage. However, as for the HIFU nonlinear propagation and temperature field in human body in relation to practice HIFU therapy, there are few studies on numerical simulation based on models conforming to practical situation. In this study, we report a numerical method of finite difference time domain (FDTD) for analyzing HIFU temperature field in human body tissues and demonstrate it through a model of 3D breast tissues. The calculation of HIFU propagation in human body tissues is done using Euler's equation of motion and continuity, which combines nonlinear ultrasound propagation with a bulk modulus and an attenuation parameter. The Pennes Bio-heat transfer equation is used to calculate temperature distribution. The simulation results of the temperature field of HIFU in human body tissues in case of different excitation function frequency and excitation function average ultrasound power densities (USPD) are reported.

Future wireless communication systems ought to offer a high spectral efficiency and an inherent flexibility to carry diverse services with variable rate requirements. The rate change should be made scalable, continuous and real-time based to match exactly to the required data rate for conservation of precious bandwidth. The rate change in multiples of two, as implemented in the existing 3G W-CDMA standard, is undesirable. It is also preferred that the multiple access technique itself should support asymmetrical traffic in up- and down-links to fit connection modes of the Internet services. This paper is a review of our recent research effort to propose an innovative CDMA architecture based on complete complementary codes, which can satisfy major requirements for the future mobile Internet applications. The architecture uses a new "offset stacked" spreading technique, based on which both high spectral efficiency and scalable rate-matching are guaranteed. To measure spectral efficiency of the systems, "spreading efficiency" (SE) is defined as the information bit(s) conveyed by each chip. All traditional CDMA-based standards offer an SE of 1/N, where N is the processing gain. On the contrary, the SE of the proposed architecture can be made as high as one. As the bandwidth of a CDMA system is determined by its chip width, a high SE means a high spectral efficiency. This paper illustrates that the proposed scheme is well-performing and has a great potential for applications in future wireless communications beyond 3G.

Code reuse multiple access (CRMA) is a new communication technique (patent pending) that employs direct sequence spread spectrum signaling for the access channel. It is similar to the spread ALOHA CDMA (SA/CDMA) and spread ALOHA multiple access (SAMA) multiple access techniques. The value of CRMA is that it improves on the multiple access collision performance of SAMA without the additional complexity required for SA/CDMA. It also removes some of the limitations of SAMA, since the spreading codes are not required to be maximal length codes of data symbol length. We compare the network throughput of CRMA to SAMA and to an equivalent multi-channel ALOHA system. We also discuss the combination of CRMA with ViaSat's patented paired carrier multiple access (PCMA) technique.

A semiconductor laser diode direct detection optical communication system suitable for use in an intersatellite communication link was constructed, and its performance was measured. The system used Q = 4 pulse position modulation (PPM) to transmit binary source data at a rate of 25 Mbit/s and contained a low-noise silicon avalanche photodiode (APD) as a photodetector. Use of the conventional Gaussian model for the output of the low-noise APD (RCA C30902S) was shown to be inappropriate under low-background radiation levels because its use caused a severe underestimate of the optical APD gain and an overestimate of a system bit error rate. A numerical procedure was developed that made use of the Conradi distribution for the APD output which gave good agreement with the results of the experimental measurements of system performance. A slot clock recovery subsystem was also provided in the receiver. It consisted of a nonlinearity which is easy to implement and a narrow bandpass filter centered at the slot clock frequency. Use of the recovered timing signal showed no penalty in the minimal input optical power required to maintain a specified error rate. The system achieved a bit error rate of 10−6 at a received signal level corresponding to an average of 60 detected photons per transmitted information bit (120 photons per PPM symbol).

In this paper, we study transmit codebook designs for spatial modulation with analog phase shifters. The proposed spatial modulation with analog phase shifters can send more spatial symbols than conventional spatial modulation, while reserving the low complexity of single RF-chain MIMO structure. The main idea is to transmit N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> different phase-shifted copies of a digitally modulated signal through N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> transmit antennas. In each time slot, the transmitted information bits are divided into two groups. The first group of the bits is mapped to the digitally modulated signal symbol. The second group of the bits is mapped to the spatial symbol, which determines the phase shift of each antenna. The transmit signal designs are carried out in open loop and closed loop scenarios, respectively. In open loop scenario, the transmit codebook is designed in two steps, i.e., generate the optimal spatial codebook according to Grassmannian line packing criterion, and find the optimal tradeoff between the cardinality of spatial codebook and the modulation order of signal symbol. In the closed loop scenario, the transmit codebook is designed according to the structure of Huffman tree. Extensive simulation results are given to validate the effectiveness of the proposed scheme in open loop scenario and close loop scenario, respectively.

The conventional matched filter (MF) correlation receiver for direct sequence spread spectrum transmissions is reconsidered from the theoretical point of view of robust distributed detection (decision fusion). Separate chip-by-chip decisions on the transmitted information bit of interest are generated. The individual decisions are then optimally fused to produce the final decision on the transmitted bit. It is proven that the majority-vote strategy is the statistically optimal fusion rule for additive white Gaussian noise channels. An exact closed form expression is given for the probability of error induced by the majority-vote receiver. It is shown that the performance is independent of the identity of the active interfering user population, that is signatures and signature cross-correlations, in DS-CDMA environments. This perfect robustness with respect to the identity of the multiuser interference component is coupled by significant resistance toward occasional high-power jamming (equivalently occasional natural severe channel imperfections) or outlier-prone background noise, or both. Some numerical studies illustrate these theoretical findings.

Transmission efficiency, defined as the ratio of successfully transmitted information bits to overall bits transmitted, can be used for evaluating the transmission performance of wireless links. As a function of received signal to noise ratio (SNR), transmission efficiency is determined by physical layer technologies, such as channel coding, interleaving, modulation and other error-recovery techniques of wireless links. In this paper we first analyze the form of transmission efficiency function in wireless links, then based on that we propose an adaptive coding scheme that maximizes the transmission efficiency according to wireless channel conditions (received SNR). Simulation results show that with the proposed adaptive coding, transmission efficiency of wireless links can be significantly enhanced.

Multiantenna transmission using load modulated arrays (LMAs) is gaining recent research interest. LMAs use a single central power amplifier and tune the antenna loads according to the information signal. In this paper, we propose a novel multiantenna transmitter architecture that can enable high-rate transmissions using LMAs. The proposed architecture uses channel modulation with RF mirrors in conjunction with antenna load modulation to transmit information bits. The proposed architecture has two key advantages: 1) it facilitates simple construction of high-rate signal sets suited for LMAs, and 2) it requires significantly fewer channel coefficients to be estimated at the receiver compared to conventional channel modulation architectures. The proposed architecture is shown to achieve improved bit error performance compared to conventional load modulation as well as spatial modulation, which are also single power amplifier transmission schemes. We also investigate the use of the proposed transmission scheme in a multiuser setting on the uplink. The proposed scheme not only offers the advantage of RF hardware simplicity at the user equipment but also requires fewer receive antennas at the base station to achieve a target bit error performance.

An adaptive coded modulation (ACM) scheme for a frequency-flat fading channel utilizes a set of channel codes with different spectral efficiencies. A feedback channel between the decoder and encoder makes it possible for the encoder to switch adaptively between these codes based on channel state information (CSI) fed back from the decoder. An orthogonal frequency division multiplexing (OFDM) system may utilize ACM on its subchannels to obtain a large average spectral efficiency (ASE), measured in transmitted information bits per second per unit bandwidth. In this paper we present a new upper bound on the ASE of OFDM/ACM systems. We also discuss how CSI estimation errors will influence the performance of an ACM system, and limit its possible region of operation with regard to channel signal-to-noise ratios and terminal velocities. (5 pages)

Frequency-hopped multiple-access communication systems employing Reed-Solomon (RS) coded M-ary FSK signalling is considered on a Rayleigh fading channel. The authors examine the optimal modulation alphabet size that maximises the average number of successfully transmitted information bits per dimension in connection with the channel traffic, the signal-to-noise ratio, and the required bit error probability.

We design and assess some practical low-density parity-check (LDPC) coded transmission schemes for the Gaussian broadcast channel with confidential messages (BCC). This channel model is different from the classical wiretap channel model as the unauthorized receiver (Eve) must be able to decode some part of the information. Hence, the reliability and security targets are different from those of the wiretap channel. In order to design and assess practical coding schemes, we use the error rate as a metric of the performance achieved by the authorized receiver (Bob) and the unauthorized receiver (Eve). We study the system feasibility, and show that two different levels of protection against noise are required on the public and the secret messages. This can be achieved in two ways: i) by using LDPC codes with unequal error protection (UEP) of the transmitted information bits or ii) by using two classical non-UEP LDPC codes with different rates. We compare these two approaches and show that, for the considered examples, the solution exploiting UEP LDPC codes is more efficient than that using non-UEP LDPC codes.