Modeling, Simulation of Multi Standard Wireless Receivers in MATLAB/SIMULINK

Brajesh Pandey Electronics and Communication Discipline

PDPM IIITDM Jabalpur Jabalpur, India

brajeshp@iiitdmj.ac.in

Abstract— We present modeling of different block sets of direct conversion receiver in SIMULINK tool-kit environment for wireless local area network (WLAN) applications. Main block set of RF receiver circuit viz. low noise amplifiers (LNA), mixers, oscillators, filters and programmable gain amplifiers are implemented. While modeling different block sets, we have incorporated both ideal and non-ideal characteristics. Main incorporated non-idealities are due to thermal noise, characterized by the noise figure and the signal-to-noise ratio (SNR) non-linearity due to second order input-intercept point (IIP2) and third-order input intercept points (IIP3). Complete RF receiver for 4G standard is implemented. Our results show that SNR of RF receiver is improved compared to similar other implementations. Gain and noise parameters have been discussed at different frequencies to show usefulness of our work. Keywords- Radio Frequency (RF); Low noise amplifier (LNA); Wireless local area network (WLAN); In phase and Quadrature phase (I/Q); Direct conversion receiver (DCR)

I. INTRODUCTION Wireless cellular communications are relatively new technology which has developed recently [1]. Earlier wireless communication was based on analog modules and then on digital modules proving data rates of upto 10 Kbps with GSM. Now a day wireless cellular phones are used for multimedia transmission with data rate upto 2 Mbps using UMTS. Improvement in wireless communication utility runs in parallel with VLSI device capabilities. New technologies help in reducing cost, size and power consumption. Use of digital circuitry has alleviated the software programmability of wireless systems for different standards for single modules which are also known as software defined radios[2]. There exists different standards like GSM, Bluetooth, GPS, WCDMA, WLAN, WiMAX [3]. The GSM (Global System for Mobile communications) standard provides the voice transmission and low speed data in the remote areas; The Bluetooth standard realizes the short-distance communication; The GPS position system is widely used in the vehicle equipment; The WCDMA (Wideband Code Division Multiple Access) standard realizes the medium speed data connection; The WLAN(Wireless Local Area Networks, IEEE 802.11x) standard provides the high-speed data and is widely used in

the urban areas, companies and home. The WiMAX [4] standard makes up the gaps between the WLAN hotspots and wide area networks. So there is need of single portable device common to all standards. The reconfigurable multi-mode receiver frontend can down-convert the RF signal into base-band. The performances and power requirements for the different standards are met by regulating the parameters of the modules [5]. This paper focuses on modeling of RF transceivers for multi-standard telecommunication [6] systems implementation in the MATLAB/SIMULINK environment which is widely used by engineers due to its direct access to many powerful tools of signal processing, data manipulation. The blocks have been modeled keeping in mind thermal noise and non-linearity. In this paper, section II explains the different building blocks, implemented in the SIMULINK. Section III deals with 4G receiver architecture and its working for different standards. Section IV discuss results obtained and in the final section we have concluded our work.

II. RECEIVER IMPLIMENTATION

A. Amplifier: It is used to amplify the input signal from preceding stages. LNA and PGA are acting as amplifier in our design [7] Fig.1. It consists of the blocks that includes the non-linear characteristic like IIP2 and IIP3 of the amplifier followed by a Gaussian noise source which is added at the output node of the block as shown in the Fig. 2.

Fig. 1. Block Diagram of Amplifier

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2013 7th Asia Modelling Symposium

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2013 7th Asia Modelling Symposium

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DOI 10.1109/AMS.2013.25

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The non-linear function is modeled, by behavioral equation (1).

Fig. 2. Sub-system of Amplifier

Fig. 3. Block diagram of mixer

B. Mixer Mixer, in addition to multiplication of the input signals in the time domain, the model incorporates a non-linear block and an additive thermal noise source similar to the amplifier model. There is an additional gain path known as direct feed through effect caused by mismatch-induced symmetries in mixer shown in Fig.3.

C. Filter Similar to mixers and amplifier, filter is used to separate the desired band of frequencies to next stages which attenuates the signal for next stage which is amplified using voltage gain as shown in Fig 4. Low-pass for baseband or band-pass for RF is used alongwith main synthesis methods using Butterworth, Chebyshev, Cauer and Bessel. Fig. 4 shows the eighth order Butterworth bandpass filter.

D. Oscilllator Quadrature oscillators have been incorporated in the tool-box. There are two important errors included in the model: I/Q imbalance and phase noise. I/Q imbalance model

is available in library and has been directly used as shown in fig.5. Phase Noise is generated by an additive noise source, digitally filtered and added to the phase of the original signal.

E. Antenna The model used for the antenna includes the test signal (composed of two tones) and an additive thermal noise source. The test signal is different depending on the test applied to verify the corresponding standard figures. In the case of multi-standard receivers, a switch block is needed to model the connection of separate RF paths, one per standard. This block is modeled as a non-linear block in a similar way to amplifiers, mixers and filters as shown in Fig.6.

Fig. 4. Block Diagram of Filter.

Fig. 5. Block diagram of Oscillator

.

III. 4G CONVERSION RECEIVER The direct-conversion receiver has been modeled and implemented using the building blocks described in section II above with the help of SIMULINK toolbox as shown in Fig.7.This receiver architecture is commonly used in multi-standard applications eliminating the need for both IF and image-reject filtering, and requires only a single oscillator and mixer [8]. In order to cope with the requirements of the different standards, separate RF hardware paths each for one standard are used whereas a single baseband section (from the mixer to the PGA) is implemented [9]. This block is implemented by simply including a non-linear function and additive noise similarly to an amplifier of unity gain. In the case under study, the multi-standard receiver fulfills the performance requirements of four standards: GSM, Bluetooth, UMTS and WLAN [10]. These receiver requirements are normally mapped onto building block specifications (gain, dynamic range, linearity, and noise figure) in an iterative synthesis process, generally referred to as receiver planning. A complete receiver planning has been done by connecting the proposed toolbox with an optimization tool, in which every building block specification is a design

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parameter that has to be obtained for given specifications. The DCR in Fig.8 has been simulated considering the building-block specifications shown in Table 1. Different test signals are applied in order to verify the receiver performance according to the standard specifications. As an illustration, Fig.9 depicts the level diagram of these signals when they are propagated through the receiver chain. The main performance metrics of RF receivers are Noise figure (NF), IIP2 and IIP3 [11].

Fig. 6. Block Diagram of Antenna

Fig. 7. Block diagram of 4G Receiver

Fig. 8. Multi standard DCR

IV. RESULTS AND DISCUSSION

As shown in figure, results are modeled using Simulink MATLAB and comparisons with the previously published studies on WLAN standards for direct-conversion receiver are plotted in Fig.9 below. We have significantly improved the gain of LNA. The overall noise of the system was also found to be higher. But, the SNR was observed to be improved. The behavioral models of the building blocks, including their main non-ideal effects, have been incorporated in MATLAB by combining SIMULINK library elementary blocks.

Fig. 9. Power analysis and comparison

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Fig. 10. Input to ADC for following cases: a)w=31.4Giga-rad/s, b)w=62.8Giga-rad/s, c)w=92.4Giga-rad/s

Power Spectral Density (Gain and Noise) plots were observed at varying operating frequencies in the RF range (2-10 GHz) for WLAN standards as shown in Fig.10. A qualitative study of the plots in terms of change of gain and noise was done.

V. CONCLUSION It was inferred from the plots that the gain was maximum in the mid-frequency range around 6GHz whereas it dropped in both high as well as low frequencies. On the other hand, noise showed a linear pattern decreasing by increasing frequency and the SNR found was maximum in the mid-frequency range. A quantitative study of the noise can further be performed thereby modeling the noise with respect to operating frequency. Also, the noise of the overall system can be reduced by using feedback linearization of the LNA.

REFERENCES

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[3] 802.11 IEEE Standard for Wireless Local Area Networks, 2005: [4] Noriharu Suematsu, “Si-RFIC Technologies for Multi-Band Multi-

Mode Wireless Terminals,” CJMW, pp 1-4, April 2011. [5] G. Gielen and E. Goris, “Reconfigurable Front-End Architectures and

A/D Converters for Flexible Wireless Transceivers for 4G Radios” Proc. of the CAS Symposium on Emerging Technologies: Circuits and Systems for 4G Mobile Wireless Communications, pp. 13-18, June 2005.

[6] A. Morgado, V.J. Rivas, R. del Ro, R. Castro-Lpez, F. Fernndez and J.M. de la Rosa, “Behavioral Modeling, Simulation and Synthesis of Multistandard Wireless Receivers in MATLAB/SIMULINK,” VLSI2007, July2009.

[7] X. Li and M. Ismail, Multi-Standard CMOS Wireless Design Kluwer Academic Publishers, 2002.

[8] Asad A. Abidi, “Direct-conversion radio transceivers for digital communications,” IEEE J. of Solid-State Circuits, Vol. 30, pp. 1399-1410, Dec. 1995.

[9] E. Mensink, D. Schinkel, E. Klumperinck, “A 0.28pJ/b 2Gb/s/ch Transceiver in 90nm CMOS for 10mm On-chip interconnects,” ISSCC Dig. Tech. Papers, pp. 314-315, Dec. 2007.

[10] H.-K. Yoon and M. Ismail, “ A CMOS Multi-standard Receiver Architecture for ISM and UNII Band Applications,”Proc. IEEE Int. Symp. Circuits and Systems, pp. IV.265-268, 2004.

[11] J. Andrews, W. Choi, and R. Heath, Jr., “Overcoming Interference in Spatial Multiplexing MIMO Cellular Networks,” IEEE Wireless Commun., vol. 14, no. 6, pp. 95104, Dec. 2007.

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