GB2440165A

GB2440165A - Real-time signal generation apparatus for radio receiver testing

Info

Publication number: GB2440165A
Application number: GB0614448A
Authority: GB
Inventors: Neil Brownlow White; Brian Gardner; Robert Charles Robinson
Original assignee: Racal Instruments Wireless Solutions Ltd
Current assignee: Aeroflex Burnham Ltd
Priority date: 2006-07-20
Filing date: 2006-07-20
Publication date: 2008-01-23
Anticipated expiration: 2026-07-20
Also published as: GB2440165B; GB0614448D0

Abstract

A real-time signal generation apparatus is used to test a radio receiver having N receive antennas (N > 1). The apparatus includes M digital signal sources (1), (M > 1), each emulating an output of a respective radio transmitter and N groups of M digital multipath fading simulators (3), the simulators of each group deriving digital multipath faded signals from the outputs of the digital signal sources (1). The digital multipath faded signals of each group are combined (4) and noise (5) is added to the resultant combination signals which are all then convened (6) to RF analogue signals to be received by the receive antennas of the radio receiver under test.

Description

A REAL-TIME SIGNAL GENERATION APPARATUS

This invention relates to a real-time signal generation apparatus, particularly for testing a radio receiver.

A radio receiver normally operates in conditions of interference and multiple time-varying propagation paths. In order to validate the performance of a radio receiver prior to field deployment, it can be tested using an apparatus to emulate the signal source, and an apparatus to simulate the radio propagation conditions, normally referred to as a "fading simulator" and "noise generator". Such apparatus is commercially available and typically operates with analogue (radio frequency) input and output interfaces to give generic applicability. Most fading simulators operate by converting the radio frequency input to a digital baseband signal, convolving with the channel impulse response, and then converting back to an analogue radio frequency signal.

However, radio systems operate most efficiently under conditions of diversity, and commercial cellular radio systems (e.g. UMTS) are beginning to exploit spatial diversity and multiple-input, multiple- output architectures. These architectures have multiple transmit and receive antennas, and in field deployment, will have multiple independent propagation paths between each antenna. Traditional fading simulators are not well suited to testing these systems for the following reasons: *5 * Multiple antennas require multiple radio frequency down-conversion and up-conversion stages, increasing the cost of the fading simulator.

* The signal source emulator must provide multiple radio frequency outputs for input to the fading simulator, increasing the cost of the source emulator.

* Combining/splitting all the analogue signals degrades the accuracy with which the test signal can be defined.

* It is difficult to synchronise the signal sources, multiple fading simulators and noise generators to reproduce an identical test signal.

* Different test scenarios require re-cabling of the analogue signals.

In addition, conventional fading simulators have limited dynamic capability, normally allowing only a static combination of transmitter/receiver relative velocity and path delay. This only provides a limited test of the receiver's ability to detect, track and demodulate each radio propagation path.

The invention relates to real-time signal generation apparatus including digital signal sources representing the radio transmitters, digital multipath fading simulators representing the propagation paths, and, optionally, digital noise generators representing the interfering sources. All signals are calculated in real-time, i.e. they are not retrieved from pre-stored tables or files and are generated at a rate matched to the consumption rate of the receiver under test. The resulting digital signals are either consumed in digital form by the radio receiver under test using the receiver's own clock, or are converted to analogue RF signals suitable for direct input to receive antenna(s) of the radio receiver under test.

Accordingly, the invention provides a real-time signal generation apparatus for testing a radio receiver having N receive antennas, where N?!, the apparatus comprising, M digital signal sources, where M?1 each emulating an output of a respective radio transmitter where the digital signals output by the source(s) are calculated in real-time, up to N groups of up to M digital multipath fading simulators, the or each multipath fading simulator of a group being arranged to derive a digital multipath faded signal, emulating a propagation path, from an output of a respective said digital signal source where the propagation path characteristics are calculated in real-time, and output means for presenting said digital multipath faded signal(s) to the receive antenna input(s) of the radio receiver under test.

The digital components of the apparatus can be inherently synchronised using, for example, first-in-first-out memories to transfer data between clock domains. The master clock source is either the digital to analogue converter, which runs at a fixed rate, or in the case where samples are consumed by the radio receiver under test in digital form, the clock of the receiver under test. As a result of this synchronisation, the generated signal is completely reproducible.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings of which: Figure 1 is a block diagram showing a real-time signal generation apparatus according to the invention, and Figure 2 is a block diagram showing a multipath fading simulator used in the apparatus shown in Figure 1.

Referring to Figure 1, the apparatus includes M (M?1) digital signal sources 1, where each digital signal source emulates the output of I of M transmit antennas.

These signals then go into a flexible routing/duplication fabric 2 where they are distributed to N blocks of M digital multipath fading simulators 3, where N (N>l) is the number of receive antennas on the radio receiver being tested, and MxN is the total number of multipath fading simulators. The outputs of the fading simulators are added together in the flexible combination fabric 4 to produce N digital baseband signals for transmission. Then noise (typically white Gaussian noise) from an interference or noise source 5 is added to each of the N signals and they are converted in converter 6 to analogue RF signals that are suitable for direct input to the antennas 7 of the radio receiver under test.

Figure 2 illustrates one of the M x N digital multipath fading simulators 3 in greater detail. One of the digital signal sources 1 generates a digital input signal emulating the output of a transmit antenna and this is distributed via the routing/duplication fabric 2 to T (T>l) tap units 30 of the multipath fading simulator 3, each tap unit emulating a radio propagation channel which may consist of multiple paths arriving at the same time instant. A real-time velocity generator S supplies relative transmitter/receiver velocity information to all tap units 30 and this velocity information is used as an input parameter by a Rayleighlpure Doppler gain generator 31 and a constant/periodic/lognormal gain generator 32 in each tap unit 30. The outputs of the gain generators 31,32 are multiplied by the digital input signal in a multiplier 33 to apply a time-variable path gain to the input signal. A real-time constant/periodic/pseudo-random delay generator 34 calculates an instantaneous time delay which is applied to the digital input signal by a time delay 35 after the time-variable path gain has been applied in multiplier 34. Finally, the resultant digital outputs produced by all the tap units of the multipath fading simulator 3 are added together in summation unit 9 to produce a digital multipath faded signal available as output on line 10.

The described apparatus differs advantageously from known apparatus in that its components operate in real-time; and so there is no need to cycle though parameter tables calculated in advance. In particular, the transmitter/receiver relative velocity parameter and the propagation path gain and delay parameters used in the multipath fading simulators 3 are calculated in real time and are time-variable giving substantial dynamic capability, whereas hitherto such parameters have usually been fixed for a given test scenario.

Also, the digital signal sources, multipath fading simulators and noise sources of the apparatus are all synchronised for repeatability and the use of combination fabric allows emulation of multiple transmit antennas without the need for additional analogue RF conversion stages.

Further advantages of the described apparatus include a significant reduction of equipment costs, especially when there are more transmit than receive antennas, improved relative level accuracy due to processing in the digital domain, improved reproducibility of test signals due to inherent synchronisation of digital components, improved dynamic capability enabling the dynamic performance of a radio receiver to be explored using time-variable relative velocity, gain and delay parameters in the multipath fading simulators and improved adapability due to the modular nature of the apparatus and use of flexible routing/duplication and combination fabrics which allow the apparatus to be expanded (or contracted) arbitrarily to suit a desired test scenario.

Claims

CLAIMS

1. A real-time signal generation apparatus for testing a radio receiver having N receive antennas, where N>1, the apparatus comprising, M digital signal sources, where M>l, each emulating an output of a respective radio transmitter, where digital signals output by the source(s) are calculated in real time, Up to N groups of up to M digital multipath fading simulators, the or each multipath fading simulator of a group being arranged to derive a digital multipath faded signal, emulating a propagation path, from an output of a respective said digital signal source, where the propagation path characteristics are calculated in real time, and output means for presenting said digital multipath faded signal(s) to the receive antenna input(s) of the radio receiver under test.

2. An apparatus as claimed in claim 1 wherein said output means is arranged to present said multipath faded signal(s) in digital form to the receive antenna input(s) of the radio receiver under test.

3. An apparatus as claimed in claim 1 wherein said output means derives from said multipath faded signal(s) an analogue RF signal(s) to be received by the receive antenna input(s) of the radio receiver under test.

4. An apparatus as claimed in any one of claims Ito 3 wherein said output means includes means for digitally combining digital multipath faded signals of the or each said group before they are presented to the receive antenna input(s) of the radio receiver under test.

5. An apparatus as claimed in anyone of claims I to 4 including digital interference sources for adding noise to said digital multipath faded signal(s).

6. An apparatus as claimed in any one of claims 1 to 5 including N digital interference sources, corresponding to the N receive antenna(s), wherein the or each said interference source adds noise to a respective combination signal.

7. An apparatus as claimed in any one of claims 1 to 6 wherein said digital multipath faded signals are combined in flexible combination fabric allowing connection to said multipath fading simulators to be flexibly reallocated.

8. An apparatus as claimed in any one of claims Ito 7 wherein said digital signal sources and said multipath fading simulators are connected together by flexible routing/duplication fabric allowing connections between said sources and said simulators to be flexibly reallocated.

9. An apparatus as claimed in any one of claims 1 to 8 wherein said digital signal sources are baseband digital signal sources. l0

10. An apparatus as claimed in any one of claims 1 to 9 wherein the or each said multipath fading simulator includes a plurality of taps, each said tap including a real-time gain generator and a real-time delay generator for respectively applying a time-variable gain and a time-variable delay to an output of a said digital signal source whereby to produce a digital output, and means for combining the digital outputs of the taps to generate a said digital multipath faded signal.

11. An apparatus as claimed in claim 10 wherein said real-time gain generator includes a Rayleigh or pure Doppler gain generator and a constant, periodic or log-normal gain generator.

12. An apparatus as claimed in claim 11 wherein the output of each said gain generator is responsive to an output of a constant or periodic transmitter/receiver relative velocity generator.

13. An apparatus as claimed in claim 12 wherein the output of each said gain generator and the output of said velocity generator is a time-variable output.

14. An apparatus as claimed in any one of claims I to 13 wherein digital signals are represented by complex Cartesian or poiar (real and imaginary or amplitude and phase) digital values at baseband (0Hz or any frequency offset) which are time-variable and are calculated in real-time.

15. An apparatus as claimed any one of claims 1 to 14 wherein said digital source(s) and said digital multipath fading simulator(s) are synchronised such that the digital multipath faded signal(s) are repeatable with a predetermined precision.

16. An apparatus as claimed in claim 15 wherein said sources and simulators are synchronised either directly in the same clock domain or individually via FIFOs spanning multiple clock domains.

17. An apparatus as claimed in any one of claims 1 to 13 having a modular configuation allowing the values of M and N to be selected.

II

18. An apparatus substantially as herein described with reference to the accompanying drawings.