Smart Antenna Testbed Project

SMART ANTENNA TESTBED PROJECT

Introduction

The 3rd generation (3G) mobile communications systems, are based on wideband code division multiple access (W-CDMA) technology. The 3G systems will have to handle multi- rate mixed traffic, comprising not only the plain voice users, but also the high-rate multimedia data users. To maintain acceptable system capacity and network performance, tight power control must be carried out both for the data users and for the voice users. However, tight power control is not only expensive but also difficult to achieve. Furthermore, power control alone cannot address the issue of power imbalance between high rate and low rate users.

The above problems in 3G systems can be effectively tackled by using smart antennas. Since there are normally only a few high rate users but many low rate users, nulls can be directed towards the high rate data users and, as a result, the signal quality for the low rate users will be greatly improved. Alternatively, more users can be accommodated in the same network. On the other hand, main beams can also be directed at the high rate users to reduce the interference from the "mass" of low rate users. The latter solution can be more desirable given the fact that high rate users generally have to bear a lower processing gain. Finally, the accuracy requirement for the overall power control can also be relaxed.

Objectives

A smart antenna test bed will be developed, and smart- antenna algorithms for CDMA will be implemented. The blind adaptive algorithms implemented on the smart antenna system are Least- Squares Despread -Respread Multi Target Array (LS-DRMTA) and Least- Squares Despread - Respread Multi Target Constant Modulus Algorithm (LS-DRMTCMA). BER and beamforming performance of the algorithms will be investigated under the conditions,

· Timing offset between local generated and received PN sequence. · Frequency offset between local oscillator and the carrier of impinging signal. · Imperfect power control.

Smart Antenna Test Bed

Our aim is to prepare a set-up, as shown in the Figure 1.1, to implement blind adaptive smart- antenna algorithms for CDMA. A two user and two receiver system has been set up and 3rd receiver will be added later. The smart antenna system consists of two-signal generators, and transmit antennas, Fig. 1.2, two receiver-chains with half wavelength spaced two-element antenna array and a computer to process captured data in Matlab, Fig.1.3.

Figure 1.2- Signal generator and transmit antenna.

Signal generators generate BPSK modulated signal for two users at 1,92 Mchips, at carrier frequency of 2.125 GHz. Figure 1.3- Two-element antenna array, 2 receiver chain and a computer to process captured data.

The receiving module includes two microstrip inset patch antennas, two -receiver chains, Fig. 1.4. Each receiver chain makes the conversion from RF to baseband, samples it at 40 Msamples/s with 10-bit precision sends the samples to computer by means of network interface module for post processing in Matlab.

Figure 1.4- Microstrip inset patch antennas and two -receiver chains