Implementation Techniques for Broadband Radio Channel Simulators

Transcription

1 Implementation Techniques for Broadband Radio Channel Simulators Jochen Schütz Elektrobit GmbH Munich / Germany Tommi Jämsä Elektrobit Oy Oulu / Finland OUTLINE general information on radio channel simulators increasing bandwidth and dynamic range some measurement results Implementation Techniques for Broadband Radio Channel Simulators 1

2 Implementation Techniques software simulators widely used, but extremely slow compared to to real-time simulators analogue hardware simple implementation, low number of of path, simulation repeatability is is poor digital hardware operates in in real-time, repeatable tests, provides accurate controlling, digital signal processing can be be done by by a DSP processor or or by by hardware Implementation Techniques for Broadband Radio Channel Simulators 2

3 Calculation speed Channel Impulse Response h(t) real-time convolution y(t) number of multiplications per second M: h y L () () j () t t = β φ t e [ t () t ] i δ τ i= 1 () t = x() t h( t) i i M = 4 f S L Implementation Techniques for Broadband Radio Channel Simulators 3

4 Tapped Delay Line Model x (t) τ... 1 τ 2 τ 3 τ L-1 g (t) 1 g (t) g (t) 2 g (t) 3 4 g (t) L Σ y (t) Implementation Techniques for Broadband Radio Channel Simulators 4

5 Functional Block Diagram of the RF Simulator RF input Quadrature Down Converter ADC Digital Baseband Processing DAC Quadrature Up Converter RF output Multipath fading is done in digital domain to archieve the best possible accuracy, flexibility and repeatability. Implementation Techniques for Broadband Radio Channel Simulators 5

6 RF, ABB and DBB Interfaces Transmitter Fading Simulator Receiver RF tests DBB DAC UC DC ADC DBB DAC UC DC ADC DBB Analog baseband tests DBB DAC ADC DBB DAC ADC DBB Digital baseband tests * ASIC * FPGA * SW DBB DBB DBB Implementation Techniques for Broadband Radio Channel Simulators 6

7 Simulator Plug-In Units GPIB Ethernet Display Keyboard Mouse SCU BBU RFU BBU RFU... BBU RFU ABB ABB ABB DBB RF DBB RF DBB RF Implementation Techniques for Broadband Radio Channel Simulators

8 Bandwidth and Dynamic Range some systems needs high dynamic range (e.g. OFDM systems with high peak to average power ratio) several components limiting system bandwidth and dynamic range (e.g. A/D and D/A converter) problem: high speed and high dynamic range are competing against each other solution: good converters and very accurate BB components and an accurate converter board design, good grounding is needed for high dynamics Implementation Techniques for Broadband Radio Channel Simulators 8

9 Increasing RF Bandwidth RF parts and digital circuits limit also bandwidth, therefore very wideband RF parts are needed and noise performance and linearity must be excellent. In RF simulation there is one additional way to increase bandwidth by using RF splitting and combining. Implementation Techniques for Broadband Radio Channel Simulators 9

10 Splitting RF Band to increase RF BW RFLO #2 RFLO #2 RFLO #1 RFLO #N RFLO #1 RFLO #N Fading Channel Wideband RF input RF Splitter Fading Channel RF Combiner Wideband RF output Fading Channel offers testing and simulation of extemely wideband systems fading channels can be different, more freedom in channel modelling Implementation Techniques for Broadband Radio Channel Simulators 10

11 Frequency Response Frequency response of whole simulator (from RF input to RF output) is measured. axis represents frequency, measurement span is 100 MHz. Y axis shows amplitude in the scale of 2 db/division. Peak-to-Peak gain variation in 70 MHz RF band is less than 2 db. Implementation Techniques for Broadband Radio Channel Simulators 11

12 Input dynamic range Input dynamic range is measured by attenuating RF input level in 10 db steps in 90 db range. Output power was measured from RF output by network analyzer with IF filter of 30 Hz. One can see that dynamic range is over 70 db. Implementation Techniques for Broadband Radio Channel Simulators 12

13 Fading dynamic range Fading dynamic range is measured by connecting constant signal level to simulator RF input and attenuating tap coefficients in 10 db steps in 50 db range. RF output level was measured. Implementation Techniques for Broadband Radio Channel Simulators 13

14 RF Splitting Split RF band was also tested. It gives over 140 MHz bandwidth when two adjacent RF channels are used. Measured frequency response of two channels is shown. Implementation Techniques for Broadband Radio Channel Simulators 14

15 ... any questions? Key Features 8 independant channels RF / ABB / DBB interfaces 70 MHz MHz for adaptive antenna tests multistandard systems geolocation applications supports GSM, 3GPP, Hiperlan2... Implementation Techniques for Broadband Radio Channel Simulators 15