Ashvin Chheda

Power control methods for dedicated control channels during discontinuous transmission in IS-2000 systems

We address the problem of power control for dedicated control channels (DCCHs) in IS-2000 CDMA networks during intervals of discontinuous transmission (DTX). A receiver must have the ability to distinguish between a bad traffic frame and a stoppage of transmission, if outer loop power control (OLPC) is to operate properly. We propose two new methods to facilitate the detection of a DTX interval. The first method uses measurements of the signal-to-noise ratios of the traffic channel and the power control sub-channel. The second uses explicit signaling between the transmitter and receiver. Simulations are used to assess the performance of the first method.

A performance comparison of the CDMA IS-95B and IS-95A soft handoff algorithms

Code division multiple access (CDMA) networks typically register high occurrences of soft handoff. Handoff is warranted when signal diversity is essential, ensuring that grade of service (GOS) criteria and capacity requirements are met. However, excess handoff can reduce network capacity and increase base station (BTS) hardware requirements. The IS95B soft handoff procedure attempts to dynamically reject excess soft handoff. This paper compares the performance of the IS95B soft handoff procedure to its predecessor, IS95A, via a combined physical and network layer simulator. The results indicate that the IS95B soft handoff procedure has the ability to reduce and maintain the average Walsh code per user and hardware elements per user to near constant levels as network loading drops. However, it does not provide any capacity gain over IS95A when operating the network at 1% call blocking levels.

On the forward link capacity of a cdma2000-1X system with transmit diversity

The capacity gain expected from next generation CDMA (IS-2000) voice networks over current (IS-95) networks is attributed to fast forward power control and transmit diversity. We compare the forward link capacity of IS-2000 to IS-95 for 9600 bps voice traffic. Three transmit diversity schemes are considered: orthogonal transmit diversity (OTD), phase sweeping transmit diversity (PSTD), and space-time spreading (STS). The study indicates that IS-2000 radio configuration 4 (RC4) with STS will maximize capacity over IS-95. This gain is 5.5 dB when averaged over the two IMT-2000 pedestrian channel models; and 1.5 dB when averaged over the two IMT-2000 vehicular models. Due to lower rate convolutional coding, RC3 users will require lower forward link power than RC4 users. However, the fewer Walsh codes in RC3 will likely lower RC3 Erlang capacity below RC4 Erlang capacity at typical system blocking levels (1-5%).

Performance evaluation of two transmit diversity techniques for cdma2000

This paper compares the performance of two transmit diversity schemes, orthogonal transmit diversity (OTD) and phase sweeping transmit diversity (PSTD), when utilized by the cdma2000 forward link. Each scheme is simulated for one- and two-path Rayleigh fading channels, and for a one-path Rician fading channel with different k-factors. For configurations employing a coding rate of 1/2 , it is shown that PSTD can significantly outperform OTD when the fading is Rayleigh distributed. For configurations using a coding rate of 1/3, the two methods provide similar performance under Rayleigh fading conditions. Under Rician fading conditions, OTD provides gain over PSTD for both code rates. The gain increases for higher k-factors.

Performance of fast forward link power control for CDMA systems

Fast power control is being considered on the forward link for the third generation CDMA systems. This paper simulates fast power control on the forward link for a 9600 bps data rate and discusses potential capacity gains. Performance of the fast power control scheme for 800 and 1600 Hz power control update rates are given to determine the potential capacity improvements as the update rate is increased. The paper also discusses some of the issues that need to be considered in designing fast power control for the forward link.

Evaluation of performance improvement of IS-2000-A in comparison to IS-2000

IS-2000 Release 0 is the standard for the first phase of cdma2000, a 3G wireless technology. Release 0 allows a maximum single channel rate of 153.6 kb/s. The next release, IS-2000 Release A, was introduced to improve the performance of cdma2000. A key enhancement increases the maximum single channel rate to 307.2 kb/s. We evaluate the performance benefits of this higher data rate feature. Simulations show there is no significant sector throughput increase. The increase in user throughput depends on system loading, and for highly loaded systems the gain is small. We analyze the dependency of throughput gain on the system power loading, and discuss the channel rate distribution and other characteristics of system performance. We provide recommendations to maximize the benefits of the 307.2 kb/s channel and identify configurations that will not benefit from 307.2 kb/s.

On multi-cell interference and capacity of the CDMA forward link with tracking beam antennae

The use of narrow tracking beam antennas at base stations provides a way to increase the capacity of CDMA cellular systems. The realistic capacity evaluation of such a system is still a challenge since multi-cell interference is hard to model, especially considering real-time power control and soft handoff. This paper proposes and compares both an analytical and a simulation approach in calculating multi-cell interference in the CDMA forward link with a transmission tracking beam antenna. The analytical method assumes a constant required E/sub b//N/sub 0/ for all users in the system to maintain a given quality of service, while the simulation approach takes the CDMA soft (and softer) handoff gain into account. The results show that the latter yields a more realistic interference power profile. To evaluate the capacity gain of the tracking beam system, the interference power profile is incorporated into an IS-2000 symbol-level user motion simulation. The simulations show that narrow tracking beam antennas can provide about 2.7 times capacity gain over a conventional tri-sector system.

Capacity comparison of packet options in IS-2000 with various power control methods

A capacity comparison of packet options P1 and P2 in IS-2000 is presented in this paper. We first describe some power control methods applicable to the dedicated control channel (DCCH) during intervals of discontinuous transmission (DTX). Then a capacity comparison is made with various power control methods under a web browsing traffic model. The results show that, in general, P2 has a capacity advantage over PI. The results also indicate that the capacity comparison between packet options P1 and P2 is a function of the timer from active state to dormant state as well as the length of data duration.

A spectral efficiency comparison of UMTS-FDD and 1xRTT cdma2000 for voice services

Third-generation (3G) cellular technologies are designed to carry more traffic than their second-generation (2G) predecessors. Spectral efficiency for voice services is compared between two competing technologies by simulation of their physical layer wireless transmission under IMT-2000 channel conditions. Assuming 25% of mobiles at 3 km/hr, 37.5% at 30 km/hr, and 37.5% at 100 km/hr, UMTS 12.2 kb/s AMR speech with spreading factor 128 is 0.78 dB more spectrally efficient than 8.6 kb/s 1xRTT RC4 (radio configuration 4) speech. UMTS 10.2 kb/s with spreading factor 128 is 0.6 dB more efficient, while UMTS 7.95 kb/s AMR speech with spreading factor 256 is 0.72 dB less efficient, than RC4. 1xRTT 8.6 kb/s RC3 speech is 0.98 dB more efficient than RC4. These calculations assume sufficient OVSF (orthogonal variable spreading factor)/Walsh codes exist in the system. Thus, efficiency is based on power utilization rather than code depletion.

Capacity of cdma2000 fixed wireless access system with transmit diversity

The capacity gain expected from next generation CDMA (IS-2000) fixed wireless access (FWA) networks over current (IS-95) FWA networks is attributed to various factors e.g. fast forward power control and transmit diversity. We study the forward link capacity of a FWA system based on IS-2000 technology for voice traffic with and without space-time spreading (STS) transmit diversity. The study indicates that an urban IS-2000 FWA system using STS can carry about 10-12% more traffic than an urban IS-2000 FWA system not implementing transmit diversity. In suburban environments the gain from STS is on the order of 50%. FWA systems using IS-2000 without transmit diversity can carry about 23% more traffic per sector in the suburban environments than the urban environments. In all these cases we have assumed that sufficient Walsh codes exist to support the carried traffic. In practice, the finite number of Walsh codes may limit the capacity of many FWA systems.