Vieri Vanghi

LTE-Advanced: Heterogeneous networks

Long-Term Evolution (LTE) allows operators to use new and wider spectrum and complements 3G networks with higher data rates, lower latency and a flat IP-based architecture. To further improve broadband user experience in a ubiquitous and cost effective manner, 3GPP has been working on various aspects in the framework of LTE Advanced. Since radio link performance is approaching theoretical limits with 3G enhancements and LTE, the next performance leap in wireless networks will come from the network topology. LTE Advanced is about improving spectral efficiency per unit area. Using a mix of macro, pico, femto and relay base-stations, heterogeneous networks enable flexible and low-cost deployments and provide a uniform broadband experience to users anywhere in the network. This paper discusses the need for an alternative deployment model or topology using heterogeneous networks. To enhance the performance of these networks, advanced techniques are described which are needed to manage and control interference and deliver the full benefits of such networks. Range extension allows more user terminals to benefit directly from low-power base-stations such as picos, femtos, and relays. Adaptive inter-cell interference coordination provides smart resource allocation amongst interfering cells and improves inter-cell fairness in a heterogeneous network. In addition, the performance gains with heterogeneous networks using an example macro/pico network are shown.

Soft interference cancellation in multiuser communications

AbstractIn this paper the performance of soft interference cancellation in synchronous multiuser channels is investigated. Two-stage detection with decorrelator in the first stage is considered. Soft first stage tentative decisions are formed by means of a multilevel quantizer or linear clipper. The asymptotic multiuser efficiency (AME) is used as a performance measured for optimization of the nonlinearity. It is shown, for the two-user case, that soft interference cancellation by means of an optimized linear clipper achieves the AME of the maximum likelihood detector if the crosscorrelation of the signature waveforms is less than

Frequency Coordination Between UMTS and GSM Systems at 900 MHZ

1/\sqrt 2

Inter-system handoff between wireless communication networks of different radio access technologies

. For the K-user case, novel upper bounds on the AME for two-stage detectors with feedback interference cancellation, with both hard and soft tentative decisions, are obtained. The derived bounds are used to examine the performance of two-stage detectors in a cellular scenario.

The cdma2000 System for Mobile Communications: 3G Wireless Evolution

In WCDMA [3 GPP G. T. 25.211, 1990], downlink channel indicators are used in a variety of procedures related to access and paging. A binary indicator is sent on the paging indicator channel (PICH) in a mobile station (MS) is paged. A ternary indicator is sent on the access indicator channel (AICH) when the MS attempts to access the network. While underlying motivations for using paging and access indicators are different, they both share same key performance aspects: detection reliability at the cell edge and downlink capacity consumption. This paper details a framework for PICH and AICH performance analysis. Results are derived that are of practical interest to the network operator for downlink transmit power budgeting.

User equipment centric mechanism for enabling 2g/3g preferred camping

UTRA-FDD requirements for operation in the 900 MHz band have been recently standardized in 3 GPP paving the way for refarming of GSM spectrum to UMTS. UMTS900 networks will have to co-exist with GSM900 networks for some time. 3GPP (2005) has studied co-existence issues and has concluded that GSM900 and UMTS900 can co-exist in both coordinated and un-coordinated deployments in which the UMTS900 carrier is allocated 5 MHz in addition to a guard-band equal to 1 GSM channel (200 KHz) on each side. However, in some deployments the operator may not have sufficient available GSM spectrum to allow the GSM traffic to be offloaded from the spectrum allocated to UMTS900 to the remaining GSM spectrum. Hence of interest is to assess system performance under much more stringent spectrum clearing assumptions. Here we characterize transmitter and receiver performance based on lab tests conducted on commercial equipment, both UMTS900 and GSM900 terminals and base stations. From such measurements we assess the impact of mutual interference, GSM MS with UMTS NodeB and UMTS UE with GSM BTS, on receiver performance as a function of frequency offset and coupling loss between interfering transmitter and offended receiver. We show that the limiting factor is the interference caused by the GSM MS to the UMTS Node B, and that as little as 4.2 MHz of GSM spectrum can be cleared and allocated to one UMTS carrier with satisfactory system performance.