Software Defined Radio Technology -- Part 3

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Offline najnin

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Software Defined Radio Technology -- Part 3
« on: May 08, 2014, 11:49:11 AM »
In this part, we would like to show the MATLAB Simulink Model for SDR,

Fig 1: Packet/payload formulation model

The access code is 72 bits and used to detect the presence of a packet. The header is 54 bits that contains information associated with the packet and the link control. The payload ranges from zero to a maximum of 2745 bits.

In packet access code, the preamble is a fixed zero-one pattern of 4 symbols used to detect edges of received data. It should be 1010 or 0101, the synchronization (SYNC) word is used for time synchronization, while the trailer is combination of 6-append-bits and 4-trailer-bits should be 1100101010 or 0011010101.

In payload encoding block the 136 bits are input from the source is overlapped by 8 bit payload
header which is protected by CRC -16-CCITT, the resulting 160 bits sent to the encoding block where the 2/3 forward error correction (FEC) is applied to produce a total of 240 encoded bits. The 10-bit header info isprotected by the 8 bit CRC which is then encoded by 1/3 FEC results in total of 54 bits.

The header information is then concatenated with the 72 bits access code and the 240 payload encoded bits resulting in completion of 366 bits packet.

Fig 2: Frequency hopping spread spectrum model

FCC regulations for FHSS devices requires devices to hop over at least 75 channels and limit the maximum bandwidth of each hopping channel to 1MHz. The hop selection kernel as shown in Fig. 2,
addresses a register containing the RF channel indices those refer to 79 RF channels ranging 2.402GHz - 2.480GHz. The inputs A to D determines the ordering within the segment, the inputs E and F determine the mapping onto the hop frequencies. The X input determines the phase in the 32-hop segment, whereas Y1and Y2select the time slots between master-to-slave and slave-to-master for time division duplex.

Fig 3: Packet modulation & transmission over USRP2 model

GFSK Modulation: FCC regulations for FHSS devices requires devices to hop over at least 75
channels and limit the maximum bandwidth of each hopping channel to 1MHz. The hop selection kernel as shown in Fig. 3, addresses a register containing the RF channel indices those refer to 79 RF channels ranging 2.402GHz - 2.480GHz. The inputs A to D determines the ordering within the segment, the inputs E and F determine the mapping onto the hop frequencies. The X input determines the phase in the 32-hop segment, whereas Y1and Y2select the time slots between
master-to-slave and slave-to-master for time division duplex.

According to FCC rule the system follows the modulation characteristics; the modulation index µis between 0.28 and 0.35, with a bandwidth-bit period product BT=0.5, for a symbol rate of 1 Ms/s, which corresponding to a data rate of 1 Mb/s, while the minimum frequency deviation is greater than 115 kHz.

Fig 4: Transmission spectrum view

In USRP2 interpolation and decimation is an integer value between 1 and 512. The interpolation and decimation rates, in combination with the sampling rate of the DAC/ADC, determine the data rate in Simulink. The sampling rate of the USRP2 device is 100 MHz, so an interpolation rate of 512
results in a Simulink sample time of 512/100e6.

Reference:
1. Building Software-Defined Radios in MATLAB Simulink
– A Step Towards Cognitive Radios

Ahmad Ali Tabassam, Farhan Azmat Ali
Department of Information Technology (INTEC)
Gent University
9000 – Gent, Belgium

Sumit Kalsait, Muhammad Uzair Suleman
Business Unit Automation, Research & Development
Phoenix Contact Electronics GmbH
32657 – Lemgo, Germany
« Last Edit: May 08, 2014, 11:53:12 AM by najnin »