1. Case Study (ZigBee): Phase IV Transmitter & Receiver Simulation

2.  The standard specifies the following four PHYs: 1. An 868/915 MHz direct sequence spread spectrum (DSSS) PHY employing binary phase-shift keying (BPSK) modulation 2. An 868/915 MHz DSSS PHY employing offset quadrature phase-shift keying (O-QPSK) modulation 3. An 868/915 MHz parallel sequence spread spectrum (PSSS) PHY employing BPSK and amplitude shift keying (ASK) modulation 4. A 2450 MHz DSSS PHY employing O-QPSK modulation 3/3/20162

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5. 5 The functional block diagram below is provided as a reference for specifying the 868/915 MHz band BPSK PHY modulation and spreading functions. Each bit in the PPDU shall be processed through the differential encoding, bit-to-chip mapping and modulation functions in octet-wise order, beginning with the Preamble field and ending with the last octet of the PSDU.

6.  Differential encoding is the modulo-2 addition (exclusive or) of a raw data bit with the previous encoded bit. This is performed by the transmitter and can be described by the following Equation : E n = R n ⊕ E n–1  where Rn is the raw data bit being encoded En is the corresponding differentially encoded bit En–1 is the previous differentially encoded bit  For each packet transmitted, R1 is the first raw data bit to be encoded and E0 is assumed to be zero.  Conversely, the decoding process, as performed at the receiver, can be described by: R n = E n ⊕ E n–1 6

7.  Each input bit shall be mapped into a 15-chip PN sequence as specified in the below Table: 7

8.  The chip sequences are modulated onto the carrier using BPSK with raised cosine pulse shaping (roll-off factor = 1) where a chip value of one corresponds to a positive pulse and a chip value of zero corresponds to a negative pulse. The chip rate is 300 kchip/s for the 868 MHz band and 600 kchip/s in the 915 MHz band. 8

9.  The raised cosine pulse shape (roll-off factor = 1) used to represent each baseband chip is described by: 9

10.  Discrete Multipath fading channel  The channel parameters are:  1- Sampling time is 1/(20KHz * 15 bits/code * 16 samples/bit) = 2.1e-7  2- Maximum Doppler frequency: ▪ Indoor: λ= 3000000/868000000 = 0.3452 m let the speed indoor be 2 m/sec so fd = 2/ λ = 6 Hz  Outdoor: let the speed outdoor be 100 km/hr = 28 m/sec so fd = 28/ λ = 80 Hz  3- Path delays: We can make multiple paths  4- Power for each path is given as pdp.  Delay between paths = 8 samples = 0.5 *T s  Signal Bandwidth (Lowpass equivalent) B s = 10 kHz  Symbol time, T s = 1/B s = 0.1 msec  Data Rate = 20k sym/sec  Sampling rate = 4.8M samples/sec  Samples/symbol = 16 3/3/201610

11.  First, random data is generated.  The data is differentially encoded.  DSSS (bit to code) mapping is done according to the table in the standard.  Then BPSK modulation is done.  Data is upsampled by 16 (16 samples per symbol).  Modulated data is filtered using pulse shaping filter of raised cosine with rolloff factor = 1 The delay of because of the pulse shaping filter is 128 samples.  The pulse shaped data is passed through fading channel.  AWGN noise is added.  Data is downsampled. The delay for the faded channel and the pulse shaping filter is compensated.  Data is demodulated using BPSKDemodulation.  Data is decoded for the differential encoding done at the transmitter.  BER is computed 3/3/201611

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16. 3/3/201616 One-path FC three-path FC five-path FC

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18.  IEEE standard for 802.15.4 2006 3/3/201618

19. THANK YOU 3/3/201619