Space-time Division Multiple Access Research Articles

Benefits of the sparsity of mmWave outdoor spatial channels for beamforming and interference cancellation

Future outdoor communication networks are expected to make use of the mmWave bands. In this context, this paper investigates the use of sparse signal processing for efficient angular frequency estimation. Compressive sensing (CS) and correlation-based method are shown to provide accurate estimates of the Power Angular Profile (PAP). The recovered PAP is used to perform analogue beamforming. When tracking mobile users it is shown that codebook based analogue beamforming, as used in IEEE 802.11ad, results in a large signalling overhead. This adversely affects net throughput. Our CS approach requires just 2% of the resources consumed by codebook-based beamforming while providing similar SNR performance.Interference cancellation is implemented by exploiting the accurate PAP recovered by CS. This method estimates the beamforming vector required to optimise the signal to leakage and noise ratio (SLNR), allowing the coexistence of both non-interfering and interfering links. To maximise user fairness the interference cancellation capabilities of CS beamforming are combined with a Space–Time Division Multiple Access (STDMA) scheduling scheme. Considerable network throughput enhancement is demonstrated when compared to the IEEE 802.11ad codebook based beamforming approach.

Throughput enhancement of IEEE 802.11ad through space‐time division multiple access scheduling of multiple co‐channel networks

60-GHz millimetre-wave (mm-wave) communication is gradually becoming a promising candidate for the next generation wireless system to meet the demands of mobile applications. To compensate for high path loss, directional links are established in mm-wave communication system, which adds opportunity for spatial reuse. As one of its most promising protocols for commercial production, IEEE 802.11ad standard provides a mechanism to support space-time division multiple access (STDMA) within a single network. However, the interference level among different co-channel networks is much lower than that inside a network, which provides greater potential for spatial reuse. In this study, based on the architecture and timing structure of IEEE 802.11ad, the authors propose a spatial reuse strategy among multiple co-channel networks. They formulate the problem as a mixed-integer non-linear programming problem, and then propose an inter-network STDMA scheduling algorithm, which considers clustering frame structure in IEEE 802.11ad, and combines greedy principle and mutual interference avoidance strategy. Extensive simulation results have shown that the proposed scheme enlarges total throughput in comparison with STDMA inside each network, as well as non-STDMA scheme. Meanwhile, it achieves the lowest packet loss rate under heavy traffic load.

A New Link Scheduling Algorithm for 60 GHz-WPAN Communication System

With apparent advantages of several GHz license-free spectra, low power consumption, low-cost implementation of CMOS devices, and so forth, 60 GHz wireless communication technology becomes the first choice for short-range high rate wireless communication in future wireless personal area network (WPAN) and wireless local area network (WLAN). While different from common WPAN system with omnidirectional communication, 60 GHz-WPAN system generally adopts directional communication. In this paper, a device (DEV) interconnected mechanism of 60 GHz-WPAN based on switched beamforming technology is structured firstly. Without considering the directional transmission characteristic of 60 GHz communication, most of the 60 GHz-WPAN Medium Access Control (MAC) protocols fail to make full use of the high spatial reuse degree caused by directional communication. In this paper, an average time slot multiplexing allocation (ATSMA) algorithm based on space/time division multiple access (STDMA) solution is proposed, which allows concurrent transmission in a single time slot. The designed link schedule process includes common channel interference (CCI) probing scheme, link coexistence determination scheme, and link schedule algorithm. Extensive simulations are conducted in order to demonstrate the efficiency of proposed scheme. Simulation results demonstrated that the capacity gain is obvious using ATSMA algorithm, no matter whether under omnidirectional antenna or under directional antenna.

A new autonomous orbit determination algorithm based on inter-satellite ranging measurements

Due to the limitation of onboard computers relatively low storage and processing ability, current autonomous orbit determination (OD) algorithms mostly adopt sequential and distributed method for navigation satellite. Such algorithms can save computing resources, however have met the problem of filter divergence and rapid accuracy decline especially under the condition of less inter-satellite links (ISLs). This paper proposes a new rapid and stable centralized algorithm based on powerful high frequency inter-satellite measurement capability under the space/time-division multiple access (STDMA) system. This approach describes the difference between the real and long term forecasting orbit as the simple higher order polynomials, which needs no complex dynamic modeling, trajectory integration and the state transition matrix calculation, thus greatly saves computing resources. Meanwhile, this paper advances to make full use of the longitude of the ascending node information of forecast orbit so as to reduce the dependence on ground support system. Finally, we simulate the Beidou global constellation structure and ISL measurements, demonstrate the impact of the number of ISL, the noise of ISL on the performance of autonomous OD, and analyze the total amount of computation theoretically. The simulation results show that the algorithm with high stability has no error accumulation, and can run normally even with 3 ISLs, and under the condition of no less than 5 ISLs, the orbit user orbit error (URE) is about 0.9 m after 60 days autonomous operation. The total amount of calculation of the new method is theoretically one-seventh of the distributed extended Kalman filter algorithm.

Joint Congestion Control and Packet Scheduling in Wireless Sensor Network

Background: Congestion is the most important starting place for packet drop, escalating queuing delay, small throughput, retransmission of packets, and hence utilization of extra energy, also running down of communication resources. With the aim of surpassing this complication, Joint Congestion Control and Packet Scheduling (JCCPS) mechanism with the help of Space-Time Division Multiple Access (STDMA) is proposed in this research work. Methods: Here, an extended version which makes use of both cluster and tree based strategy is formulated. This builds a node-centric approach that makes a load balanced tree in WSNs of asymmetric structural design. Results: The proposed approach results in less congestion in the complete network, boosts the throughput and at the same time increases the packet delivery ratio (pdr) and also diminishes delay. Moreover, it also boosts network efficiency by the way of increased delivery of packets. Load balancing, network lifetime, and scalability are essential constraints for numerous data collecting sensor network applications. Furthermore, the proposed STDMA packet scheduling approach has enhanced working than the existing schedulers in accordance with the average task waiting time and end-to-end delay. Conclusion: The proposed JCCPS protocol is very effective to determine the constraints which influence the network.Keywords: Congestion Control, Clustering, Cluster Tree Topology, Load Balancing, Packet Scheduling and Congestion Control Protocol, Space-Time Division Multiple Access

Power Control Optimization Algorithm in Cognitive Radio Network

For cognitive radio environment needs of different users, A space-time diversity multi-carrier code division multiple access (OFDM-CDMA) technology architecture of the cognitive radio (CR) system is used, a novel non-cooperative power control algorithm and the price game (NPGP), in order to protect the economic interests of the spectrum of network providers, to achieve a fair and efficient allocation of spectrum resources have cognitive and improve spectrum efficiency. Simulation results show that the algorithm under the protection of the economic spectrum premise network provider benefits, both to ensure the fair and efficient allocation of spectrum resources, and achieve effective control of power users, system performance improved significantly.

Joint Routing and Scheduling in Mobile Aeronautical Ad Hoc Networks

In this paper, we formulate the joint Internet gateway allocation, routing, and scheduling problem in wireless ad hoc networks with the goal of minimizing the average packet delay in a space-time-division multiple-access (STDMA) network. We first propose a mathematical programming approach consisting of two steps: the minimization of the weighted hop count (mWHC) subject to scheduling constraints, followed by average delay minimization for the previously computed routes. Since the computational complexity of this approach is prohibitive for larger networks, we also formulate a genetic algorithm (GA) that can be applied to larger networks and mobile networks. We analyze the performance of both approaches by means of simulations and compare the solution that they provide to a simple hop-count-based routing and gateway selection solution. It is shown that the performance of the GA is comparable with the mathematical programming approach in terms of delay and packet delivery ratio (PDR) at lower complexity and is significantly better than the hop-count-based solution.

Optical Space-Time Division Multiple Access

This work presents an approach to multiple access for free-space laser communication (lasercom) called space-time division multiple access, which aggregates traffic from multiple users at the network edge. The objective is to share resources to lower the cost, size, weight, and power consumption per user, thereby making lasercom feasible for users that require only moderate average information rates. This concept relies on fast, agile electronic beam steering, which was implemented in this investigation using liquid crystal optical phased arrays. We designed and built an experimental terminal incorporating a bidirectional communication aperture that was shared among the users, and two independently operated acquisition and tracking apertures. Using two remote user terminals, experiments were conducted to measure access node performance for a variety of operating conditions traceable to anticipated applications. The transmit and receive directions of the downlink and uplink communications channels were rapidly hopped between the two users, and data were exchanged between the access node and a user while the optical channel dwelled on the latter. Results showed that the measured information throughput efficiency correlated well with model predictions and was high enough to realize the expected advantages in applications with many users. Throughput efficiencies, defined as the actual data throughput as a percentage of the throughput without multiple access, exceeded 85% for dwell times of 100 ms and greater. This translates into an average information rate of 400 Mb/s for as many as 20 simultaneous users. Current optical phased arrays are capable of providing fast transitions between remote users, with values measured in the range 10-18 ms. The use of persistent tracking links was a key factor in achieving fast transitions, and it was found that motion of the remote terminals had no significant impact on performance.

A RAKE-Based Iterative Receiver for Space-Time Block-Coded Multipath CDMA

A turbo multiuser receiver is proposed for space-time block and channel-coded code division multiple access (CDMA) systems in multipath channels. The proposed receiver consists of a first stage that performs detection, space-time decoding, and multipath combining followed by a second stage that performs the channel decoding. A reduced complexity receiver suitable for systems with large numbers of transmitter antennas is obtained by performing the space-time decoding along each resolvable multipath component and then diversity combining the set of space-time decoded outputs. By exchanging the soft information between the first and second stages, the receiver performance is improved via iteration. Simulation results show that while in some cases a noniterative space-time coded system may have inferior performance compared with a system without space-time coding in a multipath channel, proposed iterative schemes significantly outperform systems without space-time coding, even with only two iterations. Furthermore, the performance loss in the reduced-complexity receiver due to decoupling of interference suppression, space-time decoding, and multipath combining is very small for error rates of practical interest.

In-Cell Frequency Reuse for Broadband Indoor Wireless Systems Using Sectored Antennas

This paper proposes a hybrid Space-Time Division Multiple Access (S-TDMA) for broadband indoor wireless systems using sectored antennas. It is shown that portables which are located in different sectors of the indoor microcell may be able to reuse the same frequency and the same time slot. However this requires careful scheduling of packet transmissions in order to avoid transmitting packets that would jam each other during the same time slot. It is proposed that the scheduling be performed by the base station, i.e., a central control architecture. If the number of channels (simultaneous transmissions) is larger than two, the optimum scheduling algorithm, the one that maximizes the number of packets transmitted per frame, is in the NP-Complete class of problems and so can not be solved in real time. Therefore a sub-optimum algorithm named the First Fit Algorithm (FFA) is proposed for frame scheduling and its performance is investigated through measurement results obtained in some typical indoor environments. Computer simulations based on the measured data showed that the FFA can provide a large capacity gain. For example, for a minimum acceptable signal-to- interference ratio of 10 dB and for a sectorization level ten (using ten sectors in the base station) the FFA can multiply the capacity by 3.6 in a typical open indoor location. This means that on average, 3.6 packets can be transmitted per time slot while using the same radio frequency.

Antenna-sector time-division multiple access for broadband indoor wireless systems

This paper investigates a hybrid space-time-division multiple access (S-TDMA) for broadband indoor wireless systems using sectored antennas. It is shown that portables which are located in different sectors of an indoor microcell may be able to reuse the same frequency and the same time slot. However, this requires careful scheduling of packet transmissions in order to avoid transmitting packets that would jam each other during the same time slot. It is proposed that the scheduling be performed in the base station, i.e., a central control architecture. The optimum scheduling algorithm, the one that maximizes the number of packets transmitted per frame, may be in the NP-complete class of problems, so it cannot be solved in real time. Therefore, a suboptimum algorithm, called the first fit algorithm (FFA), is proposed for frame scheduling. It was found that the capacity gain achieved by the FFA is dependent on the capture threshold, which is defined as the minimum signal-to-interference ratio required in order to achieve a given packet error rate goal. The capture threshold depends on the modulation and coding schemes. This paper investigates the performance of the FFA operating with multicarrier trellis-coded modulation. An alternative multicarrier modulation is analyzed, and the FFA performance is investigated when operating with the alternative and with the conventional multicarrier through computer simulations based on measured data which were obtained with a sectorization level of ten (using ten antenna sectors in the base station). The simulations have shown that the FFA can provide a large capacity gain when operating with multicarrier trellis-coded modulation and using differential detection. For example, while previous schemes can transmit only one packet at a time, the proposed scheme can transmit, on average, more than four packets per time slot in an open indoor location, or close to three packets per time slot in a closed indoor location with internal walls of concrete blocks.