Forward Link Capacity Research Articles

Performance analysis of forward-link capacity in multimedia CDMA systems considering macrodiversity effect

Abstract Multimedia services need macrodiversity handoff to guarantee real-time property and quality of service (QoS). Therefore, it is important to consider macrodiversity effect in calculating forward link capacity. In this paper, a novel analytic model of forward link capacity with integrated voice/data/multimedia services is developed with taking into account the effect of macrodiversity. In our analytic model, we define capacity of a system as the available peak load while maintaining a desired service quality. From the numerical results, we can see the quantitative effects of macrodiversity in system capacity. Numerical results show that forward link capacity is affected by the power distribution ratio of multipath signal, the ratio of handoff region and the combining method. Our analytic model can be extended to various environments by adjusting given parameters.

Esquemas de ordenamiento en sistemas celulares sobrepuestos CDMA

The CDMA overlay concept, has been proposed as one alternative to take advantage of the band width available in narrowband systems. In fact, the basic idea of the CDMA overlay is to allow to wideband CDMA wave forms, to share a common spectrum with narrowband conventional wave forms. In this work, we have focused in the analysis of the performance of the forward link of the CDMA and TDMA systems when they are over laid. In our model, in order to limit the interference into the CDMA layer caused by the TDMA system, the use of notch filters has been considered. However, one draw back of the filters is that it rejects only one part of the interference generated by the TDMA system. Therefore, we have proposed two new ideas of reduction of the interference which can not be eliminated by filters; ordered hunt and real location of the slots. Finally, we present an analytical evaluation of the forward link capacity of the systems involved in the over laid process, due to this is the limiting link and as a function of the outage probabilities. Practical considerations such as power requirements, power control, handoff, the offered load for different services and scenarios are also addressed.

The Dynamic Capacity in the Forward Link of CDMA Systems With Correlated BS Powers

The forward-link capacity of a power-controlled code-division-multiple-access (CDMA) system was commonly obtained by assuming equal base-station (BS) power throughout the system and neglecting the correlation and interaction among BS powers, which is rarely true in real CDMA systems. We propose an iteratively analytical process to determine the dynamic capacity in CDMA systems with unequal BS power by considering the correlation and interaction among BS powers. Simulation results show that the Erlang capacity is significantly different by modeling the BS power as a random variate instead of a constant value. We also show that correlation among BS powers can be up to 0.13, and the reduction in Erlang capacity can be up to 30%. To efficiently evaluate the dynamic Erlang capacity and correlation among BS powers, a closed-form expression of the capacity in terms of certain outage and blocking probabilities is obtained by using the distribution of the BS power.

Admission Control Utilizing Region-Based Channel Capacity

This paper presents an admission control technique for multi-carrier systems with an FRF(frequency reuse factor) of 1. The FRF of 1 is very attrative for more improved channel throughput but the forward link capacity is rapidly decreased at the cell boundary region due to the increase in the ICI(InterCell Interference). By measuring a region-based channel capacity and deriving a closed form of blocking probability, a QoS(Quality of Service) maintenance technique and mobility model can be acquired. In the simulation, the proposed scheme demonstrates a blocking probability reduction of up to 40% compared to the cell-based link capacity scheme.

Interference analysis and capacity for forward link 3G CDMA network with adaptive antennas

AbstractIn code division multiple access (CDMA) systems, the capacity of forward link (FL) communication to mobile receivers is limited primarily by co‐channel interference (CCI). Adaptive antenna arrays (AAAs) that use antenna arrays along with advanced signal processing at the base station (BS) have been proposed to mitigate this limitation. For a 3G CDMA cellular network, where each BS equipped with an AAA serves mixture of voice and data users within its coverage, we study FL capacity and investigate the effects of different factors (array topology, multipath angle spread, data rate, and beamforming algorithm) on this capacity under Rayleigh fading channel. By modeling the instantaneous signal‐to‐interference power ratio received at the mobile, we derive the system outage equation that considers blocking of either desired voice or data user. Simulation results show that for the same element spacing and number of antenna elements per cell, the uniform circular array (UCA) topology results in larger capacity than the sectorized uniform linear array (ULA) topology does, and that a larger angle spread or data user rate reduces FL capacity. Copyright © 2007 John Wiley & Sons, Ltd.

Capacity Balancing Between the Reverse and Forward Links in Multiservice CDMA Cellular Networks With Cross-Layer Design

Capacity unbalance is a practical problem for future cellular networks where the forward link traffic and the reverse link traffic are asymmetric. In this paper, an analytical framework for balancing the reverse and forward link capacities with an adaptive soft handoff probability (SHP) scheme in multiservice code-division multiple-access cellular networks is presented. With the proposed adaptive SHP scheme, system capacity can be balanced under various reverse and forward link traffic volumes, and system performance is optimized at the optimal SHP. A cross-layer model involving the physical layer, the link layer, and the network layer is presented. SHP in the physical layer, the outage probability in the link layer, and connection admission control (CAC) schemes, including complete sharing and virtual partitioning, in the network layer are jointly considered. The quality of service metrics in the link layer, including SIR and the outage probability, is derived with the information from the physical layer. The admission region is obtained by satisfying the outage probability requirements in both the forward and reverse links. Based on the admission region, the network layer grade of service, including the new connection blocking probability, the handoff connection dropping probability, and the throughput, is formulated as the performance metrics. The optimal SHP is selected by looking for the lowest penalty of connection blocking, which counts in both new connection blocking and handoff connection dropping probabilities. The cross-influences between the selection of the optimal SHP and the CAC schemes are also investigated. Numerical results show that the maximum achievable gain in throughput for the high-revenue services is about 80% by combining the benefits from the adaptive SHP and dynamic CAC schemes as compared to when none of these schemes is used.

Accurate Channel Estimation Method for Frequency Domain Equalization on cdma2000 High Rate Packet Data System

In order to improve the forward link capacity of cdma2000 HRPD (High Rate Packet Data) or CDMA2000 1xEV-DO, it is significant to overcome multi-path interference. This paper focuses on FDE (Frequency Domain Equalization) with MMSE (Minimum Mean Square Error) criterion. On top of that, backward compatibility with HRPD should be maintained, in other words common channels such as the pilot channel should not be changed. Thus, the PN (Pseudo Noise) spread pilot block without CP (Cyclic Prefix) signals has to be dealt with for FDE. However, this will cause the conventional channel estimation accuracy to deteriorate. In order to improve the estimation accuracy of the conventional method, this paper presents a MRC (Maximal Ratio Combining) spectrum estimator, IPI (Inter-Path Interference) canceller, and path searcher. The results obtained from computer simulations reveal that the proposed method can improve the PER (Packet Error Rate) performance significantly. If compared with Rake combiner and TDE (Time Domain Equalization) with NLMS (Normalized Least Mean Square) scheme, the maximum data rates at a fixed PER of 1% can be increased by 5 to 8 times and 1.25 to 2.67 times, respectively.

WCDMA Forward Link Capacity Improvement by Using Adaptive Antenna with Genetic Algorithm Assisted MDPC Beamforming Technique

Capacity has always been an issue to any generation of mobile communication technologies as it is always inversely proportionate to QoS (quality of service) in nature. In order to increase the mobile communication system capacity without jeopardizing the system QoS, smart antenna is usually being suggested. There are two major types of smart antenna systems; switch beam antenna and adaptive beam antenna. Adaptive antenna which has dynamic beam is better in improving the system capacity but requires more advance beam forming algorithm and requires intensive processing power. In this paper, a novel adaptive downlink beam forming technique for WCDMA system namely Minimum Downlink Power Consumption (MDPC) is introduced. This MDPC beamforming technique is assisted by Genetic Algorithm (GA) to minimize the downlink power usage at Node B. A dynamic radio network simulator was developed in Visual C++® to study the power consumption at Node B and estimate the downlink capacity improvement by implementing this novel algorithm. Simulation was done based on single micro cell environment with considering interference from the first tier. User mobility is taken into account to provide a combined evaluation of Radio Resource Management (RRM). Capacity system under various simulation scenarios was expressed in downlink outage in this study.

Capacity of Fading Channels with Quantized Channel Side Information

In this letter, we study the capacity of fading channels with perfect channel side information (CSI) at the receiver and quantized CSI at the transmitter. We present a general algorithm for the joint design of optimal quantization and power control for maximizing the forward link capacity over flat fading channels. Numerical results for Rayleigh fading are given.

Handoff effect on CDMA forward link capacity

In this letter, an analysis on CDMA forward link capacity with hard and soft handoffs, when a handoff decision is based on filtered pilot signal strengths, is provided. For the soft handoff, capacity based on three different power allocation schemes is investigated: equal power, equal signal to interference ratio and selection diversity. Contrary to previous results that soft handoff provides a capacity decrease in the CDMA forward link, it is concluded that soft handoff mitigates capacity loss due to filtering through diversity gain, and may in fact provide higher capacity.

Capacity of the WCDMA System Using High Altitude Platform Stations

In this paper, we provide a method to estimate the capacity of the wideband code division multiple access (WCDMA) scheme using High Altitude Platform Stations (HAPS), and demonstrate the results. This is to validate that the HAPS system is one of the most effective solutions to provide high quality wireless communication services, such as IMT-2000 services. We use a practical system model which describes the HAPS system most appropriately, and this leads to realistic estimation results. We estimate the reverse and forward link capacity of the HAPS WCDMA system and compare it to that of the terrestrial system. The estimation results show that the capacity of the HAPS WCDMA system is about 1.2–1.67 times larger than that of the terrestrial system.

Capacity analysis in CDMA distributed antenna systems

In this letter, the effect of maximal ratio combining (MRC)-based macrodiversity on the reverse-link and forward-link capacity in code division multiple access (CDMA)-distributed antenna systems is analyzed. The concept of virtual cell is illustrated, and the analytical outage probability expressions are derived. The present investigation shows that on the reverse link, the interference can be suppressed greatly with macrodiversity, which leads to a significant increase in capacity. However, on the forward-link, it is proven that if simulcasting is used in CDMA-distributed antenna systems, the forward-link capacity cannot increase with macrodiversity whatever power allocation scheme is adopted. Based on the analysis of the cause of capacity loss, a new transmission scheme is further presented and the optimal power allocation scheme is derived. It is shown that, in this case, the forward-link capacity increases rapidly with the number of involved distributed antennas.

Forward-Link Capacity Analysis for MC-CDMA

OFDM-based networks utilizing the frequency reuse factor of 1 may produce the severe ICI (intercell interference) at the cell boundary even though overall cell capacity is increased and network deployment is facilitated. In the forward-link, the ICI may rise above a QoS (quality of service) threshold beyond some distance from BSs (base stations). In this paper, we analyze the forward-link capacity of an MC-CDMA system as a function of the ICI according to the distance from a cell. To achieve this goal, a closed form of the outage probability is derived and utilized to obtain the accommodated number of users and system parameters.

Theoretical Study of Site Selection Diversity Transmission in DS-CDMA Cellular Mobile Radio

Single cell reuse of the same frequency, which is possible in DS-CDMA cellular systems, yields the option of site diversity to increase link capacity. In this letter, a generalized case of site diversity transmission is considered where multiple base stations (BS's) are involved in weighted transmissions with constant total transmit power to a target mobile station (MS). A general equation of conditional bit error rate (BER) is derived based on the model of weighted transmissions combined with antenna diversity reception and rake combining. It turns out theoretically that the optimum set of weights to maximize forward link capacity makes site selection diversity transmission (SSDT) the best performer. This theoretical analysis is confirmed by performance evaluation based on the Monte-Carlo simulation.

A Study on Forward Link Capacity in MC-CDMA Cellular System with MMSEC Receiver

This paper focuses on the MC-CDMA (Multi Carrier-Code Division Multiple Access) with the MMSEC (Minimum Mean Square Error Combining) receiver, which is a good candidate of a transmission scheme for beyond 3G systems. This paper evaluates the forward link capacity using the MMSEC receiver in the MC-CDMA cellular system, which employs TDM (Time Division Multiplex) transmission for multiple users. In this paper, the PDF (Probability Distribution Function) of the SINR (Symbol to Interference plus Noise energy Ratio) after MMSEC under multi-cell environment are calculated with the various number of the code division multiplexes. Based on the PDF, the numerical relation can be derived between the peak rate of the adaptive transmission and the average transmission rate per sector.

The Other-Cell Interference Calculation of Forward Link Channel in Multicode CDMA Systems

This paper analyzes the other-cell interference of forward link channel in multicode CDMA system supporting a voice and data service. In this system, voice communication can be served by a basic code and data service can be supported by multiple codes. Using this analysis, we can get the approximated capacity of forward link. We describe the effect of data user activity and received power level ratio between a data service and a voice service. Also, this paper describes the forward link capacity and the power ratio of data power to voice power according to the change of FER threshold for data service.

Benefits of the control‐hold mode for the support of the forward packet data channel in IS‐2000

AbstractThe most recent revisions of the IS‐2000 standards are being designed with the view of maximizing the achievable throughput while maintaining an acceptable Quality‐of‐Service (QoS) for the supported voice and data sessions. Revision C of the IS‐2000 standard is specifically geared towards maximizing the throughput on the forward link. However, this increase in forward link capacity requires adding new reverse link overhead channels thereby decreasing reverse link capacity. This paper describes the Control‐Hold mode designed to reduce the resource usage of reverse link overhead channels. In particular, the focus is on the DV‐control‐hold (DVCH) mode jointly proposed by Ericsson and Nortel for the 1xEVDV standard and adopted as an optional feature in the IS‐2000 standard as part of its Revision C 5. The DV‐control‐hold mode is an intermediary state between the active and dormant modes of a mobile. In this state, a mobile station uses less resources than when active and can also be quickly reactivated (typically in 20 ms). The QoS achieved for mobile stations (MSs) that use the Active‐DVCH‐Dormant state machine is compared to the performance of MSs with regular Active‐Dormant state machines. Simulation results show that the introduction of the DVCH mode increases both, the achievable forward link throughput and the number of admissible mobiles per sector. When the DVCH mode is introduced and for the typical ‘Active‐to‐Dormant’ timer values of 3 and 6 s, the number of admissible sessions per sector increases by 35% and 66% respectively, while the corresponding throughput increases by 14% and 50%. Copyright © 2003 John Wiley & Sons, Ltd.

Dynamic effects of power control on third-generation system capacity

Dynamic simulations with mobility in multi-pilot environments have been developed to assess the capacity advantages of third-generation (3G) 800 Hz forward link power control. We show that the key component of 3G power control is not the higher inner loop power control speed but the creation of a bit energy-to-noise density (Eb/Nt) setpoint-based power control loop that provides a target for the inner loop power control. This allows fast tracking of the dynamic geometry variations, including the large instantaneous changes due to handoff as well as other-cell interference, and provides significant additional capacity gains even at vehicular speeds where Rayleigh fading cannot be tracked. Three different simulation tools, at the chip, symbol, and power control group (PCG) level, all confirm the excellent performance of 3G power control, as well as the existence of additional forward link capacity with 3G power control. Although our specific examples are based on CDMA2000 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∗</sup> , similar conclusions apply to the forward link power control algorithms used in wideband code division multiple access (W-CDMA).

Correction to "Forward-link capacity of a DS/CDMA system with mixed multirate sources"

Correction to "Forward-link capacity of a DS/CDMA system with mixed multirate sources"

Forward-link performance of satellite CDMA with linear interference suppression and one-step power control

Wideband direct-sequence (DS)-code-division multiple-access (CDMA) is a strong candidate for both terrestrial and satellite components of UMTS. The forward-link capacity of a satellite DS-CDMA system with a conventional matched filter (MF) receiver is limited by interference from adjacent beams and possibly overlapping beams from multiple satellites. In this paper, we study the performance of the linear minimum mean squared error (MMSE) receiver for the satellite forward link. System constraints are long propagation delay, which prevents accurate closed-loop power control, and low on-board power consumption, which implies a low received bit energy to noise density ratio at the mobile receiver. We consider a one-step power adjustment algorithm which attempts to compensate for random shadowing and path loss, and compare the associated performance of the MMSE and MF receivers. Dual-satellite diversity is also considered. The effect of code rate on performance is studied through the use of punctured convolutional codes and the evaluation of random coding bounds. Our results indicate that linear MMSE interference suppression can improve the quality of service and increase system capacity significantly.