Design and Implementation of the Wireless LAN RF Transceiver at 5GHz Band

Transcription

1 Design and Implementation of the Wireless LAN RF Transceiver at 5GHz Band Bonghyuk Park o, Hae Won Jung, Jaejung Lee, Hyeong Ho Lee Router Technology Department, Electronics and Telecommunication Research Institute 161 Kajong-Dong, Yusong-Gu, Taejon , Korea Abstract The IEEE802.11a wireless LAN standard was released at July, The 5GHz band wireless LAN RF Front End transceiver is designed in accordance with IEEE802.11a standard and implemented with discrete RF components. In this paper, we present the structure, design and characteristics measurement of the implemented RF transceiver. The characteristics of the RF transceiver were measured at 10m distance between transmitter and receiver, and -30dBm output peak power was obtained at the receiver. 1. Introduction With the recent rapid advance in wireless communication, various applications are being appeared such as cordless, cellular, paging, data over voice, and the wireless local networking. Due to the requirement of wireless multimedia service and the rapid development of communication signal processing technique, the high rate 6~54Mbps wireless LAN standard was made in July, 1999 [1]. In 1997, FCC released the U-NII(Unlicensed-National Information Infrastructure) band for business which is used by everyone without approval. In this paper, we present the 5GHz band RF Front End transceiver system prototype which is designed and tested in the wireless LOS(Line Of Sight) channel. Before implementing the transceiver on the printed circuit board, the characteristics of transceiver are simulated using commercial software. The minimum sensitivity and noise figure is considered mainly in receiver, and the output power and ACPR(Adjacent Channel Power Rejection) is in transmitter[2]. -1-

2 Following this introduction, we describe function and structure of RF Front End system in section 2, the simulation of RF system using commercial software in section 3, transceiver measurement characteristic in wireless channel in section 4, and then discuss about future work and conclude in following section. 2. Transceiver Structure 2.1 Specification of RF Transceiver The IEEE802.11a standard suggests the following RF specification[1]. Although the IEEE802.11a suggest the 12 channels(5.15~5.35ghz, 5.725~5.825GHz), we only apply the 8channel 200MHz band for this RF Front End system. Table2.1 The Specification of RF Front End system Transmitter Receiver Parameter Requirement Parameter Requirement Frequency 5.15 ~ 5.35GHz Frequency 5.15 ~ 5.35GHz Channel Bandwidth 16.6MHz Channel Bandwidth 16.6MHz Maximum 200mW (with up to Noise Output 6dBi Ant Gain) Figure Power 10dB (5dB margin) Operating Voltage 5 V Minimum Sensitivity -74 dbm ACPR 16 db From our simulation with soft-decision viterbi decoding and channel state information, it is shown that 17.5dB Eb/No and 19.1dB SNR are needed to meet the 10-2 FER(Frame Error Rate). 8.7dB noise figure can be obtained by Equation (2.1). (2.1) Refer to the RF transceiver specification, the receiver receives the 5.15~5.35GHz RFsignalfromtheantenna,thenthissignaldown-convertto900MHz,to20MHz. 2.2 Function and structure of RF Transceiver Related to the IEEE802.11a RF Front End system, the transmitter and receiver are separated by the switch because both the transmitter and receiver are allocated same frequency band. The RF system block diagram is in Fig 2.1. The 20MHz signal is modulated with 900MHz oscillator signal and amplified by IF Amplifier. This signal is mixed with VCO( GHz signal) and then the GHz RF signal is transmitted at antenna. The same antenna is used for both transmitter and receiver. The received signal is down-converted to 900MHz IF1 signal and 20MHz IF2 signal by Mixer and Demodulator. To improve the spectrum mask characteristic, -2-

3 two saw filters is applied in receiver. The attenuator has 0dB to 38dB attenuation range, it improves the dynamic range in receiver. The RSSI(Received Signal Strength Indicator) check the received power level then send the signal to MAC(Medium Access Controller) to know whether the receiver receives the signal or not. In PLL, the 20MHz TCXO is used for reference signal, 16 Fixed Modulus divider is used for dividing the signal from the VCO. Fig2.1 Transceiver block diagram 3. Design and Simulation of RF Transceiver The output power, noise figure and ACPR characteristics are simulated by commercial software ADS. The S-parameters, noise parameters, 1dB compression point data are applied for each block. 3.1 Transmitter Design The transmitter is designed considering the output power and ACPR. Fig 3.1 shows the schematic structure of transmitter. -3-

4 Fig3.1 Schematic of Transmitter Table 3.1 shows the input power of each stage after simulating the Fig3.1. In this simulation, the input power of IF amplifier set to -10dBm. The final stage output power is 17.75dBm, so the 6dBi gain antenna is needed to meet the Transceiver specification. Table3.1 The Input Power of each Stage Fig 3.2 shows the main channel characteristic compared to adjacent channel which separate 20MHz with main channel. -4-

5 Fig 3.2 ACPR Characteristic From Fig3.2, the ACPR characteristic is more than 16dB, its value meet the IEEE802.11a specification. Fig 3.3 shows the IMD characteristic of transmitter when the two tone signal are injected at the same time. It shows more than 50dB IMD. Fig 3.3 IMD characteristic of transmitter 3.2 Receiver Design -5-

6 The receiver design focus on the noise figure and each stage gain. Fig 3.4 shows the total gain at each stage. Related to this result, the receiver can work well when the input power is injected from -74dBm to -30dBm. The total gain is 16.6dB at the input of I/Q Demodulator. Fig 3.4 Total Gain at each Stage Fig 3.5 shows the noise figure of receiver at each stage. The total receiver noise figure is less than 7dB. According to hand calculation, the required noise figure is 8.7dB including the switch and band pass filter. The 7dB noise figure is very excellent result which meet to the required specification. -6-

7 Fig 3.5 Noise Figure of Receiver at each Stage Fig 3.6 shows the whole RF transceiver simulation in wireless LOS channel. The antenna characteristic is applied in this schematic. Fig 3.7 shows the result of Fig 3.6 simulation. Fig 3.6 RE Transceiver Simulation Fig 3.7 Result of the RF Transceiver Simulation 4. RF Transceiver Measurement Fig 4.1 shows the real RF transceiver using the RO4003 substrate. The 5GHz band BPF is implemented on the printed circuit board directly using hair-pin type and patch antenna is applied. -7-

8 Fig 4.1 RF Transceiver printed circuit board Fig 4 2 shows the input signal at the I/Q Modulator and output signal at the I/Q Demodulator which measured in wireless LOS environment(10m distance). The output signal is 20dBm less than the input signal. But this output signal can be detected at A/D convener. -8-

9 Fig 4.2 RF Transceiver Characteristic in Wireless LOS Channel 5. Conclusion In this paper, we presented the RF Front End transceiver that has been designed and implemented in accordance with the IEEE802.11a specification. The -30dBm output peak power is measured at the receiver. Because the physical size of our RF transceiver is a little larger than needed for PCMCIA card, we are now developing customized MMIC chipset to reduce the transceiver physical size. -9-

10 Reference [1] IEEE a/D7.0 "High Speed Physical Layer in the 5GHz Band," [2] Peter Vizmuller, RF DESIGN GUIDE Systems, Circuits, and Equations, Artech House, [3] Behzad Razavi, RF Microelectronics, Prentice Hall PTR, [4] Bullock, Transceiver System Design for Digital Communications, NOBLE, [5] Sen-You Liu and Huey-Ru Chuang, "A 2.4GHz Transceiver RF Front-end for ISM-Band Digital Wireless Communication," Applied Microwave & Wireless, pp.32-46, June [6] T.E. Kolding, "RF Receiver Requirement for 3G W-CDMA Mobile Equipment," Microwave Journal, pp.22-46, Feb.,