Yeliz Tokgoz

VoIP over cdma2000 1xEV-DO revision A

In this article we analyze performance of VoIP services over 1xEVDO-Revision A (DO-Rev A) networks and show that high-quality VoIP with unconstrained mobility and high capacity can be achieved. Together with quality of service (QoS) requirements, we emphasize practical issues such as mobility, degradation of feedback-channel quality, and packet overheads. Novel techniques are presented for voice processing such as smart blanking and adaptive dejitter playback buffer with time warping. These techniques help to meet QoS constraints to achieve a circuit-like voice quality while improving overall capacity. Detailed end-to-end simulations are presented and system capacity is analyzed under the QoS and system stability constraints. We claim that DO-Rev A can provide VoIP capacity comparable to circuit-switched cellular CDMA technologies (e.g., IS-2000) and simultaneously carry significant amount of other types of traffic such as non-delay sensitive applications and downlink multicast.

Uplink Interference Management for HSPA+ and 1xEVDO Femtocells

Femtocells are low power cellular base stations typically deployed indoors in residential and enterprise environments as well as hotspots in order to improve voice and high rate data coverage and provide excellent user experience. The cellular operator benefits from reduced infrastructure deployment costs for capacity upgrades and coverage improvements. While improving performance, femtocells may cause some interference to other users in the network. However, with the use of proper interference management techniques, this interference may be well controlled. This paper focuses on uplink (UL) interference management techniques for 3G femtocell deployments. On the UL, the challenge is the presence of large uncontrolled interference from nearby users not associated by the femtocell that result in high noise rise (rise-over-thermal, RoT), that may lead to poor femto user experience. Femtocell users that can not be power controlled due to their very close proximity to femtocells may also cause high noise rise levels. An algorithm is proposed for both HSPA+ and 1xEVDO femtocells to desensitize the receiver when uncontrolled interference is detected, ensuring robust UL performance with minimal impact on the macro network. It is demonstrated through system level simulations that in addition to superior performance experienced by femtocell users, the macro users also benefit significantly from offloading traffic load to the femto network.

Performance analysis of maximum ratio transmission based multi-cellular MIMO systems

In this paper, we analyze the performance of the uplink of multi-cellular MIMO systems in flat Rayleigh fading. There is co-channel interference from users within the same cell as well as from other cell users. I The channel model includes lognormal shadowing and path loss along with power control, resulting in a statistical model for user powers. Consistent with practical scenarios, the co-channel interference is categorized into two groups: intracell interference from users within the same cell as the desired user and intercell interference from outer cell users. We derive a compact, easily computable closed form outage probability expression in the form of finite sums. This expression allows for simpler and faster analysis of various MIMO configurations. It has been shown that using antennas on the receiver side results in better performance, since transmit diversity does not combat interference from same cell users.

The Effect of Imperfect Channel Estimation on the Performance of Maximum Ratio Combining in the Presence of Cochannel Interference

In this paper, the effects of imperfect channel estimation on maximum ratio combining performance in receive antenna diversity systems with multiple cochannel interferers are examined. The channel considered is a slowly varying flat Rayleigh fading channel that is also spatially independent. The combiner weights are the imperfect estimates of the desired users fading coefficients and are assumed to be complex Gaussian distributed. Closed-form expressions for signal-to-interference-plus-noise ratio distribution and outage probability are obtained for both equal-power and unequal-power interferer scenarios. Using these expressions, the effect of channel estimation quality on system performance is investigated

cdma2000 Highly Detectable Pilot

Research and development on mobile phone positioning technologies are gaining momentum due to the potential in location based services. Mobile location is estimated based on measurements from satellites and terrestrial base stations. Satellite measurements often available in rural and suburban areas are less or not available in dense urban and indoor areas. Thus, base station measurements play an important role in mobile positioning. In this paper, we present the highly detectable pilot (HDP) that is being standardized in 3GPP2 for cdma2000 1xEV-DO. HDP allows mobile to detect significantly more base stations, and thus provides much better accuracy in location estimate.

On the reverse link performance of the cdma2000 1xEV-DO revision A system with antenna array receivers

cdma2000 1xEV-DO revision A (DO Rev. A), also known as IS-856-A, is a third generation (3G) wireless solution to providing wide-area high-speed mobile Internet access with high spectral efficiency and advanced quality-of-service (QoS) support. In this paper we evaluate the reverse link performance improvement (in terms of coverage and data throughput) of IS-856-A with the use of more advanced antenna array receivers. Specifically, we consider the effect of increasing the receiver antenna array size and utilizing more sophisticated beamforming schemes. We quantify the capacity improvement via analysis as well as comprehensive system simulations that incorporate realistic channel models and the dynamics associated with MAC-layer algorithms in addition to the physical-layer interactions. We show that DO Rev. A with 4-way antenna diversity on the reverse link achieves more than 3 dB gain over 2-way diversity receivers in sector throughput. We also demonstrate a coverage improvement on the order of 6 dB, which can be translated into further throughput gains by relaxing the interference control mechanism

Downlink Transmit Power Calibration for Enterprise Femtocells

Downlink transmit (Tx) power calibration is necessary in femtocell deployments to achieve a good tradeoff between downlink femtocell coverage and interference to other macrocells and femtocells. Developing a practical Tx power calibration scheme that provides excellent performance in different deployment scenarios is challenging. In this paper, we present an enterprise deployment framework that consists of coverage planning and Tx power calibration using technician assistance. The Tx power calibration algorithms presented here use mobile feedback to learn key information such as surrounding RF environment, required coverage range, and interference impact to other cells to adapt to different deployments. Both centralized and distributed Tx power calibration algorithms are evaluated for multi-femto enterprise. It is shown that the distributed algorithm, is simple, efficient and performs very close to the centralized algorithm. Furthermore, over-the-air field tests highlight the practical efficacy of the distributed algorithm in providing excellent femtocell coverage indoors with minimal leakage to outdoors.

Handoff performance analysis for 1xEV-DO Rev. A systems

We present performance analysis of handoffs on the forward link (i.e., downlink) of packet-switched 1xEV-DO Rev. A systems by a combination of theoretical analysis and simulation results. A theoretical approach is developed to evaluate slot error probability (SEP) relevant to 1xEV-DO Rev. A. The novelty of the theoretical analysis lies in the fact that unlike the existing literature we consider the combined effects of Rayleigh and shadow fading, filtering, and handoff delay on the handoff algorithm. Contrary to the general assumption, a practical filter cannot eliminate Rayleigh fading completely. We evaluate the handoff performance by considering the effects of filtering, hysteresis, and other system parameters. Tradeoffs in choosing handoff algorithm parameters are studied in terms of the SEP, packet error rate (PER), and number of handoffs.

Outage capacity improvements in multicellular CDMA systems using receive antenna diversity and fast power control

In this paper, we analyze the uplink outage capacity improvements in multicellular code-division multiple-access systems using receive antenna diversity and fast power control schemes that can track multipath fading. The channel is modeled as slowly varying Rayleigh fading with lognormal shadowing and path loss. Closed-form expressions are obtained for the outage capacity of the system by approximating the total intracell and intercell interference distributions. We show that by controlling the power level of a user at the output of the diversity combiner and imposing the condition that a user does not transmit when in a deep fade, the average intercell interference level of the system is significantly reduced. As a result of this reduction, we demonstrate both analytically and through simulations that the outage capacity of the system is improved more than linearly with increasing number of antenna elements.

Downlink interference management techniques for residential femtocells

Downlink transmit (Tx) power calibration techniques are vital in self-organizing femtocell networks to achieve a good tradeoff between femtocell coverage and interference impact to nearby macrocells and femtocells. In this paper, we present two power calibration techniques that adapt to a wide variety of residential deployment scenarios: (1) Over a long term, Tx power is adapted by learning required coverage range, RF profile inside the home and interference outside using feedback from home users and macro users; (2) Tx power is adapted in real-time based on short term dynamic variations in traffic such as arrival of active macro users (guest or passer-by). The presence of nearby active macro users is detected by sensing their uplink channel. The algorithms are shown to provide superior performance compared to conventional techniques in wide variety of deployment scenarios.