Emerging optical code-division multiple access communicationsystems

All-optical systems, which perform signal processing functions optically so that the signal conversion from optical to electrical is done only when desired, are considered. Three such schemes are discussed, namely, fiber-optic code-division multiple-access (CDMA) systems, neuromorphic CDMA systems, and ultrashort-light-pulse CDMA systems. Fiber-optic CDMA systems in which incoherent optical signal processing techniques are used to establish optical CDMA systems are first examined. In particular, a novel class of sequences for incoherent fiber-optic CDMA systems, called optical orthogonal codes, are discussed. The codes are then applied to neuromorphic optical systems, and various applications of the networks are examined. Recent experiments that demonstrate the ability to encode and decode extremely fast, femtosecond optical pulses and that suggest the possibility of ultrahigh-speed CDMA systems based on ultrashort light pulses are described     

Antenna interconnection strategies for personal communicationsystems

Microcellular and distributed antenna systems are two promising candidates for implementing personal communication systems. Antenna interconnection strategies for these systems are studied in order to determine cost-efficient as well as robust and flexible architectures in hexagonal layouts. To this end, some results from minimal networks theory are used, in particular, those dealing with the problem of Steiner trees. The significant reduction in conduit and cable lengths that the Steiner minimal tree (SMT) architecture provides over the star type, especially in large networks, is demonstrated. It is further shown that the SMT architecture also provides more flexibility and robustness compared to the star type. The suboptimal, but easy-to-construct, minimal spanning tree (MST) architecture is given as well, and it is compared to the SMT and star types     

Prioritized resource assignment for mobile cellular communicationsystems with mixed services and platform types

The proliferation of mobile, portable, and personal communication systems will bring a variety of offered services. Practical systems that are envisioned must support different types of calls. These may include voice only, mixed voice and data, high-speed data, low-speed data, image transmission, and an array of intelligent network services. In addition there may be a mixture of platforms (such as persons, autos, buses, trains, boats, and planes) having a range of mobility characteristics. In such environments, the bandwidth and/or resources needed for different call sessions will not be identical. As a result, calls will generally encounter different blocking and hand-off constraints. These effects are in addition to differences in blocking and forced (call) termination probabilities that are attributable to differing platform mobilities and (resource) channel quotas. Cellular systems with mixed platforms that support calls with differing resource requirements are considered. Loss-type systems and hybrid delay-loss systems are treated. In each case, priority access to resources for hand-off calls is allowable. We identify a suitable state characterization and framework for a performance analysis that enables numerical computation of theoretical performance results. Example performance characteristics are obtained. These show carried traffic, blocking probability, and forced termination probability for each platform type and for each call type     

Performance evaluation for multichannel access schemes in CDMA cellular systems

The CDMA system promisingly provides more capacity than AMPS. However, providing multichannels for a CDMA system is a requisite to satisfy the demanded capacity. In this paper, five schemes of multichannel assignment are proposed. Based on computer simulation, performance measures such as blocking probabilities, the overall capacity, the capacity of each channel and the number of retrials are obtained. Simulation results indicate that the SIR-based selection scheme is preferable to the other schemes. © 1998 John Wiley & Sons, Ltd.     

Digital modulation techniques for mobile and personal communicationsystems

The paper describes in detail various digital modulation techniques for mobile and personal communication systems. Among others, these include π/4-shift quadrature phase-shift keying (QPSK), used in the second generation digital cellular mobile systems in North America and Japan, and Gaussian minimum-shift keying (GMSK), employed in the GSM system in Europe. It then briefly discusses the current research activities in modulation schemes for future systems     

Two-stage ensemble paging strategy for cellular communicationsystems

Instead of per user basis, we propose a simple paging strategy based on the consideration of ensemble paging channel resource of each cell. Using only the information of the last known locations of mobile subscribers, the proposed paging scheme under a maximum delay constraint can improve the system performance (discovery rate, blocking rate, and average paging delay) significantly in the heavy load     

Power control considerations for DS/CDMA personal communicationsystems

A model of the personal communication system (PCS) employing code division multiple access (CDMA) is presented and analyzed. In the analysis, the effect of multipath transmissions that are usually present in the portable environments is included. This effect causes severe fading degradation in the received signal power. The model introduces the factors that mostly affect the reception of different signals at the base station, and their effect on the received power is discussed. The performance of the system is measured by the probability of error and the increase in the amount of power (the power cost) necessary to overcome multipath fading effects. Upper bounds on the probability of error are obtained to show the limits on the performance     

A comparison of reverse link access schemes for next-generation cellular systems

We consider different transmission options on the reverse link of cellular systems for packet data. The different transmission options are classified based on the nature of in-cell and out-of-cell interference power statistics. The categories are: (a) no in-cell interference, averaged out-of cell interference; (b) no in-cell interference, bursty out-of-cell interference; and (c) averaged in-cell interference, averaged out-of-cell interference. Depending on whether the reverse link transmission is time multiplexed one user at a time transmission, or simultaneous transmission by multiple users with or without in-cell orthogonality, the interference structure falls into one of the above three categories. We analyze the throughput performance of the system in each of these cases when incremental redundancy is employed to combat uncertainty in the interference power. We compare the different options under an in-cell rise-over-thermal (IROT) constraint and provide some insights for reverse link design for next-generation cellular systems. Our results show that transmission option (a) with an optimal choice of the number of simultaneous transmissions within the cell has the best performance over several different scenarios. Time-multiplexed transmissions, despite the bursty out-of-cell interference power structure, has throughput comparable to that of a multiple-user orthogonal transmission system for small cells where mobiles have sufficient transmit power to meet the target IROT.     

Packet reservation multiple access in a metropolitan microcellularradio environment

The author examines the performance of a packet reservation multiple access (PRMA) protocol in a metropolitan microcellular radio environment using computer simulations. Call characteristics, mobility, and channel conditions have an impact on PRMA performance which is measured in terms of the average packet dropping rate per call. In order to maintain a reasonable level of service quality for calls in progress, teletraffic loading can be controlled by introducing a call setup queue and limiting the number of active subscribers. Call mobility is found to have a minor impact on PRMA performance. PRMA is also fairly robust against adverse channel conditions with a drop in performance of about 15% when the channel packet loss rate is less than 0.01. Performance comparisons to other protocols are also carried out     

Slow frequency hopping multiple access for digital cellular radiotelephone

A theoretical analysis of slow frequency hopping is presented together with a comparison to other multiple access techniques. The propagation and modulation models are described and the multiple access protocols are analyzed with an information theory approach. It is explained why the speed of variation of some random variables is important for protocol evaluation. A definition of capacity is given and is first applied to simple systems. Full mathematical evaluations of the protocol referred to as "random SFHMA" are presented for the mobile-to-fixed-station channel, and some simulation results are given for the reverse channel. With realistic propagation parameters (α = 3.5, σ = 8 dB) and with mobile power control, there can be as many as 87 radiotelephone users per cell in a 25 MHz band. A comparison to the traditional FDMA protocol is presented and it is shown that slow frequency hopping would be more efficient for future high capacity small cell systems.     

Downlink multiple access schemes for transmitted reference pulse cluster UWB systems

Transmitted reference pulse cluster (TRPC) signaling was recently proposed for low data rate ultra‐wideband communications. Compared with the conventional transmitted reference (TR), TRPC has a more compact and uniform spacing for the reference and data pulses and therefore solves the implementation problem posed by the long delay line requirement in the conventional TR. In this paper, downlink multiple access issue is further investigated for TRPC systems. According to the TRPC signaling structure, both code division multiple access (CDMA) and time division multiple access (TDMA) methods are discussed. Theoretical analysis and simulation results show that TDMA outperforms CDMA in both bit error rate performance and throughput. Copyright © 2010 John Wiley & Sons, Ltd.     

User pairing schemes for capacity maximization in non‐orthogonal multiple access systems

This paper addresses the issues related with conventional near–far user pairing in non‐orthogonal multiple access. Performance effects of near–far pairing on regions with negligible channel gain differences between users are investigated. These regions occur when pairing is performed between cell center and cell edge users, thus leaving the cell mid users to be either paired with each other or kept unpaired. Pairing these mid users with each other causes successive interference cancelation (SIC) performance degradation resulting in capacity reduction for these users. On the other hand, leaving these mid users unpaired perfectly avoids the SIC issue but makes these users unable to benefit from the capacity gains provided by non‐orthogonal multiple access. Therefore, two user pairing strategies have been proposed that can provide capacity gains to almost all the users by accommodating them in pairs, while avoiding or minimizing the mid users pairing problem. A generalized M‐users pairing scheme is also proposed. Simulations have been performed to investigate the performance of proposed schemes for both perfect and imperfect SIC receiver scenarios in comparison with conventional pairing where the mid users are kept paired with each other. Simulation results show that proposed schemes achieve high capacity gains, especially when imperfect SIC is considered. Copyright © 2016 John Wiley & Sons, Ltd.     

The RRA‐ISA multiple access protocol with and without simple priority schemes for real‐time and data traffic in wireless cellular systems

A multiple access protocol, based on a Reservation Random Access (RRA) scheme, is derived for a wireless cellular network carrying real-time and data traffic. Given a TDMA framed channel and a cellular structure, the aim of the protocol is that of maximizing the one-step throughput over an entire frame. This is achieved by deciding on the access rights at the cell base station, which then broadcasts this information at the beginning of the frame. The decision is made on the basis of binary channel feedback information (collision/no collision) over the previous frames, as well as of long term averages of packet generation rates at the mobile stations, assuming independence in the presence of packets at the latter. The resulting protocol has therefore been termed Independent Stations Algorithm (ISA), and the overall scheme RRA-ISA. As in other RRA protocols, time constrained (e.g., voice) traffic operates in a dynamic reservation mode, by contending for a slot in the frame with the first packet of a burst, and then keeping the eventually accessed slot for the duration of the burst; packets of the time constrained traffic unable to access a slot within a maximum delay are dropped from the input buffer. No such constraint is imposed on data traffic. Together with the “basic” version of the access algorithm, three other variants are presented, which exploit three simple different priority schemes in the RRA-ISA “basic” structure, in order to give a prominence to the voice service. The aim of these variants is to improve the performance in terms of the maximum number of stations acceptable in the system, by slightly increasing the data packets delay. All the proposed schemes are analyzed by simulation in the presence of voice and data traffic. Several comparisons show a relevant performance improvement (in terms of data delay and maximum number of voice stations acceptable within a cell) over other protocols that use ALOHA as a reservation mechanism (RRA-ALOHA or PRMA schemes). This revised version was published online in June 2006 with corrections to the Cover Date.     

An access protocol for supporting multiple classes of service in alocal wireless environment

This paper presents a time split token-based contention resolution (TS-TBCR) protocol for providing multiple classes of traffic access to a shared wireless media. Since the protocol requires immediate response from the base station, it is best suited for short-range wireless applications. The key feature of the protocol is that it allows multiplexing of various services with high throughput even under heavy traffic loads. The protocol provides near perfect scheduling of information transfer by reserving a small part of the bandwidth for contention resolution. This resolves contention in an a priori manner, thus preventing collisions and leading to high channel bandwidth utilization. This protocol allows the system to support a high load while keeping packet loss probability within acceptable limits. Using a token-based mechanism, the protocol implements an access scheme, as well as a service (scheduling) discipline. The protocol is analytically modeled and extensive simulations performed to evaluate its performance. Results indicate that for multimedia traffic transport, the protocol can dynamically, and without any centralized control, realize any service discipline from first-in first-out (FIFO: complete fairness) to head-of-line (HOL: complete biasing), merely based on the relative service requirements of the traffic classes. This brings in fairness since no service class is excessively penalized     

Analytical model of busy channel multiple access (BCMA) for packetradio networks in a local environment

The performance obtainable with busy-channel multiple access (BCMA) techniques is analytically defined in the context of multichannel local radio networks. Network behavior is characterized in terms of throughput and transmission delay when a single radiofrequency channel is shared among many users, thought to be within the range of a central station, suitably located in the local area. The analytical model is based on a suitable Markov model for the generic terminal, and it is assumed that the traffic presented to the common channel conforms to a Poisson distribution. An analytical evaluation of throughput as a function of offered traffic and average transmission delay is presented. The numerical results obtained are for a particular case of BCMA, the well-known busy-tone multiple access (BTMA). In this example, the analytical model proposed allows fast performance evaluation and suitable comparison with CSMA and ALOHA protocol techniques and evaluation of the capture effect     

Novel schemes for traffic engineering in access domains

In this paper, our approach to tackling the problem of traffic engineering in access domains is discussed. The complete solution would take into account bandwidth management, allocation, de‐allocation, protection and restoration. In this work, we focus on one part of the problem, i.e. constrained routing in the MPLS access domains. We define all categories of traffic in an access domain and use CF (conjunction factor) as a figure of merit for performance evaluation of constrained routing schemes and present algorithms that control and limit CF value. The results of conducting simulations using various constrained routing algorithms are presented and conclusions are outlined. Copyright © 2006 John Wiley & Sons, Ltd.     

Dynamics of path losses between a mobile terminal and multiple basestations in a cellular environment

We investigate the dynamics of the path losses between a mobile terminal and a small group of base stations, when the mobile traverses an area containing zones where different base stations have the least path loss to the mobile. While moving through the area, the mobile measures signals transmitted by each base station. The measurements involve calculating a running average of the measured signal power over a fixed time period. It is presumed that based on these measurements and typically other inputs, the wireless network supporting the mobile makes handoff decisions. In this paper, we do not attempt to analyze the performance of a practical handoff algorithm. Instead, we focus on the average number of times per meter traveled that a moving mobile must switch base stations in order to be always served by the base station with the least path loss. The switching rate is a function of the mobiles location with respect to the base stations and the velocity of the mobile. For low velocities, the multipath fading is not averaged out completely and, therefore, affects the measured results, while at high velocities the multipath fading is averaged out, but the resolution of the measurement is compromised, and any possible handoff will be delayed (in terms of location)     

New cellular schemes for spectral efficiency

Assuming the constraint of an allocated frequency spectrum, two new schemes are suggested to increase spectral efficiency. Furthermore, the two new schemes can be integrated to become a hybrid system and offer greater performance which takes advantage of the merits and performance of each individual scheme.     

面向两层小区网络的两级跳频多址接入技术研究

为了抑制异构多层通信网络的多层干扰并保证多级服务质量(Quality of Service, QoS)需求,提出了一种新型跳频多址接入(Frequency Hpping Multiple Access, FHMA)技术。首先基于传统伪随机FH序列和数学变换给出了一类具有两级汉明相关的FH图案(FH序列集)设计方法,然后在两层小区上行链路中对采用这类FH序列的OFDM/FHMA系统的抗干扰性能和频谱效率进行了研究。信号分析和仿真结果表明,所提出的FHMA方案可以缓解两层小区的用户干扰,降低系统传输误码率(Bit Error Rate, BER),同时保证两层用户的差异化传输质量(两级BER性能和频谱效率)。该FHMA技术能够满足两层干扰抑制和多级服务质量的设计目标,这是传统伪随机FH技术难以实现的。