Mathematical analysis of dynamic channel selection in indoor mobilewireless communication systems

Dynamic channel selection (DCS) is an algorithm for flexible resource sharing in mobile radio systems. The digital enhanced cordless telecommunications (DECT) standard implements a version of DCS based on time as well as frequency multiplexing. In this paper, mathematical models are developed to evaluate the probabilities of channel availability, desired carrier power, and the carrier-to-interference ratio (CIR) for a constant traffic load. These results can be used to compute the call setup blocking probability. The models reported in this study are based on a decentralized DCS according to the DECT standard specifications. The results show that blocking due to availability of a channel (resource blocking), not interference blocking, generally is the most important factor in overall call blocking. Furthermore, it is seen that resource blocking is sensitive to the implementation of portable sets. Also, with homogeneous static traffic, this type of DCS ran be as good as fixed channel allocation (FCA) with respect to resource blocking     

A profile-based location strategy and its performance

Future microcellular personal communications systems (PCSs) will be characterized by high user density and high mobility. It is expected that registrations will incur a large amount of the radio link signaling traffic. A profile-based strategy (PBS) is proposed to reduce the signaling traffic on the radio link by increasing the intelligence within the fixed network. The system maintains a sequential list of the most likely places where each user is located. The list is ranked from the most to the least likely place where a user is found. When a call arrives for a mobile, it is paged sequentially in each location within the list. When a user moves between location areas in this list, no location update is required. The list may be provided by the user or may be based on each user's past calling history. The method for doing this is outside the scope of this work. This work focuses on the potential performance improvements that can result from maintaining such a list. This paper compares the performance of the proposed strategy to the typical geographic-based location-tracking schemes being implemented in evolving digital cellular and cordless standards. Key performance measures for the comparison are radio bandwidth, fixed network SS7 traffic, and call setup delay. We investigate the conditions under which the PBS performs better than the traditional scheme. Results indicate that over a wide range of parameters, it may be possible to reduce both the radio bandwidth and fixed network signaling load for a modest increase in call setup delay     

Cordless personal communications

The role of digital cordless technology in the transition to personal communication systems (PCSs) is discussed. The evolution of the pan-European digital cordless standards-CT2 and DECT-and industry progress in equipment availability and service implementation are reviewed. The application of cordless access to the domestic market in the United Kingdom and European telepoint, wireless PABXs, and radio drops are described. CT2 product development and availability and cordless data applications are outlined. The migration of microcellular cordless techniques for wider area systems including ETSI's universal mobile telecommunications system (UMTS) and the future public land mobile telecommunications systems (FPLMTS), now under development by CCIR with assistance from CCITT, are also discussed     

Overview of wireless personal communications

This article presents an overview of the current state of wireless communications, including relevant ongoing activities in technology development, standards, and spectrum allocation. The authors discuss cellular radio, cordless telephony, and wireless data systems. Ongoing and planned future developments are summarized. The presentation is oriented toward broad coverage rather than technical depth. However, brief discussions of the air interfaces for existing digital cellular and digital cordless systems are provided, because the air interface bears heavily on system capacity and the environments in which the system can be used, as well as on the cost and complexity of the equipment     

Ergodic Sum Rate Maximization for Underlay Spectrum Sharing with Heterogeneous Traffic

A radio resource allocation framework is proposed for underlay spectrum sharing. The ergodic capacity maximization problem in orthogonal frequency division multiple access-based network on point to multi point transmission is formulated and solved. Heterogeneous traffic is also considered in which two types of traffic is assumed: streaming traffic which has strict delay requirements, and elastic traffic with flexible delay requirements. Considering the effect of channel state information (CSI) imperfection in the evaluation of the secondary users’ expected rate, we further assume that the estimated CSI between the secondary users and secondary base station (secondary channel) is not perfect. Moreover three different cases are considered depending on the availability of the CSI between the secondary base station and the primary receivers (interference channel). Using simulations, we evaluate the impact of streaming traffic and imperfect CSI on the sum capacity of the secondary elastic users for different values of parameter systems.     

Where there's a WILL [wireless in the local loop]

Linking telephone subscribers into the network via wireless in the local loop (WILL) promises to boost telephone usage and enhance the effectiveness of telecommunications liberalisation. There is a wide choice of wireless technology potentially suitable for deployment in WILL applications. Candidates include the various analogue cellular technologies, digital cellular including GSM, and cordless systems including CT2 and DECT. The author discusses the FDMA/TDMA based fixed radio access system of Ionica, and the CDMA based system of Liberty. Both are in competition with BT. The choice of radio technology is discussed as are the problems caused by telecommunications liberalisation     

Resource allocation for cellular radio systems

High terminal traffic densities are expected in urban multiuser radio systems. An efficient allocation of resources is the key to high system capacity. In this paper, a distributed dynamic resource allocation (DDRA) scheme based on local signal and interference measurements is proposed for multiuser radio networks. It offers “soft capacity” for time division multiple access (TDMA) and frequency division multiple access (FDMA) systems, bounded above by N per base station, where N is the total number of channels in the system. The decisions are made local to a terminal and its base and are essentially independent of the rest of the system. A distributed dynamic channel assignment scheme is used to assign channels to new calls. This scheme assigns a channel that offers the maximum carrier to interference ratio (CIR) to a new call. A distributed constrained power control (DCPC) scheme based on CIR measurements is used for power control. The channel assignment scheme and the power control scheme are coupled to obtain an interactive resource allocation scheme. We compare the capacity of a system which uses the distributed dynamic resource allocation scheme described above with the capacity of a system which uses the channel assignment scheme alone. The system capacity is measured by simulation as the number of terminals that can be served by the system with a CIR above an acceptable minimum. In a 1D cellular system, coupling the channel assignment scheme with power control is discussed. Simulations were also used to show the effect of varying the maximum transmitter power on system capacity     

Emerging mobile and personal communication systems

The market demand for wireless communications has been demonstrated by the rapid growth of different second-generation wireless technologies that are optimized for particular applications and environments. Obvious examples include: digital cellular systems like GSM, ADC, PDC,and DCS1800 for widespread vehicular and pedestrian services, and cordless telecommunication systems based on CT2, DECT, and PHS standards for residential, business, and public cordless access applications. Efforts are also underway to consolidate the various radio environments and applications under a single standard for third generation wireless, i.e., FPLMTS. In the area of personal mobility, with the recent availability of “personal” numbers in various countries (e.g., 500 numbers in the United States), many fixed network operators are starting to offer such personal mobility services as “personal number service” and “number portability”. These services represent initial stages of full personal mobility that will be provided by UPT in both wireline as well as wireless environments. The expected heavy demand for PCS in the United States and the underlying market/regulatory forces are driving the standardization and business activity. A number of air interface standards for the 1900 MHZ PCS band are being considered, which are based on TDMA, CDMA, and FDMA technologies singly or in combination. Many are variations of existing digital cellular and cordless telecommunications technologies. PCS networking standards are also being developed; both for standalone systems and for systems that will utilize public switched network capabilities     

Effects of some nonuniform spatial demand profiles on mobile radio system performance

The design of future mobile radio systems will be based upon an estimated user demand. Systems probably will be engineered to serve the "average business day" spatial distribution of call attempts, which for the purpose of this study was assumed to be uniform. There will be day-to-day fluctuations about this long-term average, the magnitudes of which are only to be conjectured at this time. This paper compares the performance of computer simulated mobile radio systems operating with several demand profiles. The profiles were selected to give an indication of the effects on system performance of either uncompensated changes in average traffic or normal fluctuations which occur in the randomly offered traffic even when the long-term average value does not change. The dynamic channel assignment systems increased the traffic capacity at low blocking levels even over a perfectly designed fixed channel assignment system. In addition, it was found that the dynamic channel assignment systems were relatively insensitive to the periodic spatial demand distributions studied by this computer simulation. Even though new call attempts were made to fluctuate markedly between adjacent base stations within a reuse interval, the blocking rate of each base station remained constant. It appears that the blocking rate within a reuse interval depends (in the dynamic channel assignment systems) mainly on the average demand within that interval and not very strongly upon the distribution of that demand. In the fixed channel assignment system, uncompensated fluctuations in the spatial demand distribution away from the design value always degrade system performance.     

Relationship between performance and timing recovery mechanisms for a DECT link in dispersive channels

The performance of DECT (digital European cordless telecommunications) radio links under dispersive channel conditions is studied as a function of clock recovery strategies. It is shown that due to the non-optimal sampling, analytical and practical results based on fixed timing will not be acceptable above delay spreads of approximately 40ns. On the other hand, a burst-adaptive clock recovery scheme can more than double this range.<>     

Personal communications-a viewpoint

A personal view of an extended concept of personal communications is discussed. The relationship between low-power digital cordless technology and some alternatives (analog cordless, digital mobile radio, and cellular mobile radio) is examined. Personal communication network (PCN) power requirements, circuit quality, level of network integration, and access to network intelligence (e.g. call forwarding, call transfer, and personal number calling) are emphasized     

Interference-based channel assignment for DS-CDMA cellular systems

Link capacity is defined as the number of channels available in a link. In direct-sequence code-division multiple-access (DS-CDMA) cellular systems, this is limited by the interference present in the link. The interference is affected by many environmental factors, and, thus, the link capacity of the systems varies with the environment. Due to the varying link capacity, static channel assignment (SCA) based on fixed link capacity is not fully using the link capacity. This paper proposes a more efficient channel assignment based on the interference received at the base station (BS). In the proposed algorithm, a channel is assigned if the corresponding interference margin is less than the allowed interference, and, thus, channels are assigned adaptively to dynamically varying link capacity. Using the proposed algorithm yields more channels than using SCA in such an environment changes with nonhomogeneous traffic load or varying radio path loss. The algorithm also improves service grade by reserving channels for handoff calls     

Investigation of capacity and call admission control schemes in TD‐SCDMA uplink systems employing smart antenna techniques

Due to the TDMA (time division multiple access)/time division duplex (TDD) specialization in the uplink (UL) of code division multiplex access (CDMA) systems, some advanced techniques, such as smart antenna (SA) and multi‐user detection (MUD), are utilized conveniently in time division‐synchronous code division multiplex access (TD‐SCDMA) systems. These advanced techniques have great impacts on the capacity and radio resource management (RRM) schemes. In this paper, the UL capacity and load models specified for TD‐SCDMA systems are proposed, in which the impacts from SA and MUD techniques are considered, and the UL load can be estimated based on the total received power in the base station. According to the proposed theoretical capacity and load evaluation models, the call admission control (CAC) strategies suitable for TD‐SCDMA systems are presented. Since there are two kinds of SA schemes (i.e., tracking beam antenna (TBA) and switched beam antenna (SBA)) utilized in TD‐SCDMA systems, the efficient CAC algorithms suitable for these two SA schemes are designed and evaluated, which are based on principles of the interference increase estimation. All simulation results show that the proposed CAC strategies can work efficiently and improve performances of TD‐SCDMA systems dramatically. Copyright © 2009 John Wiley & Sons, Ltd.     

Digital cellular-its roots and its future

Cellular radio started in the early 1980s by using analog technologies. Research in voice coding, modulation, and channel coding resulted in second-generation cellular radio based on digital technologies, which were introduced in the early 1990s. These were all based on advanced time division multiple access technology, resulting in better capacity and lower cost. Today, these digital technologies-based on the Global System for Mobility, digital Advanced Mobile Phone System, and personal digital cellular-have more than 100 million subscribers worldwide. The next step is to introduce wide-band packet services for wireless Internet up to 2 Mb/s. These so-called third-generation systems (Universal Mobile Telecommunications Services, IMT2000) are planned to be introduced in the early 2000s     

Performance issues and algorithms for dynamic channel assignment

Using dynamic channel assignment (DCA) algorithms to select communications channels as needed, time-division multiple access (TDMA) or frequency-division multiple access (FDMA) systems can serve dynamic and nonuniform traffic demands without frequency planning as long as quality is sufficient and equipment is available. Here, performance issues and algorithms for DCA in a TDMA portable radio system are considered. A fixed number of traffic servers (time slots) per radio port is assumed: therefore, the system capacity is hard-limited by the equipment availability, and the DCA efficiency is compared mainly through the signal-to-interference ratio in both the uplink and downlink directions     

The Complementary Use of 3G WCDMA and GSM/GPRS Cellular Radio Networks

The traffic performance of integrated 3G wide-band code division multiple access (WCDMA) and GSM/GPRS network is evaluated. This type of network links two cellular radio systems which have different set of frequency bands and the same coverage size. The base station of 3G WCDMA is installed on an existing GSM/GPRS site. Dual-mode mobile terminals use handoff to establish calls on the better system. The soft handoff or inter-frequency hard handoff occurs when mobile terminals of 3G WCDMA or GSM/GPRS move between two adjacent cells, respectively. The inter-system hard handoffs are used between 3G WCDMA and GSM/GPRS systems. The data rate conversions between different systems, soft handoff region size, multiple data rate multimedia services, and the effect of the mobile terminal mobility on the user mean dwell time in each system are considered in the study. The simulation results demonstrate that a great traffic performance improvement on the complementary use of 3G WCDMA and GSM/GPRS cellular radio networks compared with the use of GSM/GPRS cellular radio networks. When high-data rate transmission is chosen for low-mobility subscribers, both the handoff failure probability, and carried traffic rates increase with the new call generation rate. However, both rates decrease conversely with the increasing new call generation rate as soon as the new call generation rate exceeds a critical value. This causes the integrated networks saturation. The higher mean speed for the mobile terminals produces lower new call blocking probabilities and total carried traffic. The new call blocking probabilities and total carried traffic increase with the size of the soft handoff region.     

Sampling Jitter Effect on a Reconfigurable Digital IF Transceiver to WiMAX and HSDPA

This paper outlines the time jitter effect of a sampling clock on a software‐defined radio technology‐based digital intermediate frequency (IF) transceiver for a mobile communication base station. The implemented digital IF transceiver is reconfigurable to high‐speed data packet access (HSDPA) and three bandwidth profiles: 1.75 MHz, 3.5 MHz, and 7 MHz, each incorporating the IEEE 802.16d worldwide interoperability for microwave access (WiMAX) standard. This paper examines the relationship between the signal‐to‐noise ratio (SNR) characteristics of a digital IF transceiver with an under‐sampling scheme and the sampling jitter effect on a multichannel orthogonal frequency‐division multiplexing (OFDM) signal. The simulation and experimental results show that the SNR of the OFDM system with narrower band profiles is more susceptible to sampling clock jitter than systems with relatively wider band profiles. Further, for systems with a comparable bandwidth, HSDPA outperforms WiMAX, for example, a 5 dB error vector magnitude improvement at 15 picoseconds time jitter for a bandwidth of WiMAX 3.5 MHz profile.     

Cellular CDMA capacity with out-of-band multihop relaying

In this paper, we consider the capacity of cellular code division multiple access (CDMA) when there is out-of-band ad hoc traffic relaying. The mobile stations (MSs) are dual-mode, having both ad hoc and cellular CDMA radios. An active MS is free to choose any available relay station (RS) within its ad hoc radio coverage area for dual-hop communication with the CDMA base station (BS). Communications between the RSs and the MSs use bandwidth which is available to the ad hoc radio and does not consume the CDMA capacity. Using this mechanism, CDIVIA interference can be reduced by dynamically selecting RSs which have more favorable CDMA link characteristics. Several relay station selection criteria are considered, namely, ad hoc relaying with low relative interference (ARRI), with best link gain (ARLG), and with shortest distance (ARSD). The relay station selection protocols are compatible with existing wireless local area network (WLAN) standards such as IEEE 802.11. An analytic model is used to compute the effects on uplink and downlink CDMA capacities when out-of-band relaying is added. The results show that very significant capacity improvements are possible by using these criteria compared with conventional CDMA with hard or soft handoff. Ad hoc relaying which dynamically tracks CDMA link quality can achieve greater capacity improvements than that using a distance-based relay station selection. Relaying, which considers both signal and interference conditions, achieves better capacity than that based on signal link quality alone.     

New concepts and technologies for achieving highly reliable andhigh-capacity multimedia wireless communications systems

The rapid growth of multimedia wireless communications services forces the development of advanced digital wireless systems with high reliability and high speed as well as flexibility for varying traffic conditions. To achieve such advanced wireless systems. New system design concepts different from the conventional ones aiming at increasing system capacity for voice transmission would be required. Since multimedia wireless communications require high quality, high speed, and high flexibility as well as temporary and spatial control of traffic under severe fading environments, the so-called conventional system design concept will be insufficient. New system design concepts and techniques for achieving highly reliable and high-capacity multimedia wireless communications are discussed using both time division multiple access (TDMA) and code division multiple access (CDMA) systems. The demands for high-speed and high-reliability mobile, personal, and multimedia wireless communications services strongly require matching with the trunk network constructed by a broadband optical fiber system or wired system     

Congestion relief on power-controlled CDMA networks

A digital cellular radio code-division multiple-access (CDMA) system can only support a finite number of users before the interference plus noise power density, I₀, received at the cellular base station causes an unacceptable frame-error rate. Once the maximum interference level is reached, new arrivals should be blocked. In a power-controlled CDMA system, the base station can direct mobiles to reduce their power and data rate to reduce interference and allow more users on the system. This approach is employed in TIA IS-95 with respect to the time-varying voice activity on cellular voice channels. We investigate an alternative technique where we adjust the power and data rate of mobile data users to the time-varying interference level to allow more users on a congested system. This scheme was simulated for various proportions of voice and data users and offered traffic levels. Blocking probabilities are reduced in some cases by two orders of magnitude. Message wait time, now a random variable, may exceed the wait time for a constant rate system at high traffic levels. If the cellular carrier has a maximum blocking requirement, an adaptive rate/power system can increase the capacity. For example, a base station that normally supports 26.4 Erlangs offered traffic with 2% blocking can support 33.5 Erlangs with the same blocking probability if adaptive rates and power control are used. Thus, the adaptive rate system can increase the capacity by 27%