MMSE-BASED RECEIVER BEHAVIOUR
IN HANDOVER SITUATIONS
Study of Intercell Interference
João Carlos Silva, Nuno Souto, Francisco Cercas
Instituto Superior Técnico/IT, Torre Norte 11-11, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
Rui Dinis
CAPS, Av. Rovisco Pais 1,1049-001 Lisboa, Portugal
Keywords: MMSE Equalizer, handover, MIMO, W-CDMA.
Abstract: This paper focuses on the use of an equalization-based receiver for WCDMA (Wideband Code-Division
Multiple Access) in an inter-cellular environment, for handover studies. The receiver is based on the MMSE
(Minimum Mean Square Error) algorithm and uses the UMTS (Universal Mobile Telecommunications
System) HSDPA (High Speed Downlink Packet Access) standard as a basis, alongside the reference UMTS
environments.
1 INTRODUCTION
In order to cover great areas with coverage for high
data-rate transmissions, several Base Stations (BSs)
need to be employed, with overlapping coverage
areas in order to ensure mobility without dropped
calls. These joint coverage areas are the most
troublesome areas of a cellular system, since it is
where the power levels are lower and where
significant interference from the neighboring cells is
present.
There are many occasions in which the UE (User
Equipment; e.g., mobile phone) is receiving signals
from more than one BS; when in a dense
environment it usually receives signals from a
multitude of BS, though only one or two
“interfering” BSs (Base Stations) usually present a
significant power level. In this study, two setups
were considered, one with two BSs (Figure 1), and
the other with three BSs (Figure 2).
In both setups, two positions were taken as reference.
One where the UE is receiving the same amount of
power from both BSs, and another where the UE is
closer to one of the BSs, thus receiving a higher
power level from the BS it is closer to (it is assumed
that all BSs transmit with the same power level).
Note that power control is not considered since it is
considered that the UE is only dealing with one BS.
Thus, all other Base Stations constitute interference.
For the case where the UE is at point B, it’s
considered that the signal from the closest BS
arrives 3dB higher than the other Base Stations,
whose receive power level is considered to be equal.
In each setup, two cases were considered; one where
the UE knows nothing about the messages from the
interfering BS (Single BS decoding), and the other
were the UE knows the interfering BSs codes, so it
can decode their messages in order to cancel out
their interference (Joint BS decoding). Each BS was
considered to have two transmit antennas, operating
simultaneously, in order to increase the data rate
(spatial multiplexing mode).
Figure 1: Schematic for a 2 BS setup.
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