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Range vs. Rate Comparison of Remaining IEEE 802.11g Proposals: PBCC and CCK-OFDM

Range vs. Rate Comparison of Remaining IEEE 802.11g Proposals: PBCC and CCK-OFDM. Anuj Batra, Ph . D . Matthew B. Shoemake, Ph . D . Wireless Networking Branch Texas Instruments Dallas, TX 75243. Approach.

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Range vs. Rate Comparison of Remaining IEEE 802.11g Proposals: PBCC and CCK-OFDM

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  1. Range vs. Rate Comparison of Remaining IEEE 802.11g Proposals: PBCC and CCK-OFDM Anuj Batra, Ph. D. Matthew B. Shoemake, Ph. D. Wireless Networking Branch Texas Instruments Dallas, TX 75243 Batra and Shoemake, Texas Instruments

  2. Approach • For each modulation scheme, calculate the received (Es/N0) at various distances. • Use the (Es/N0) values to look up the packet error rates (PERs) from the corresponding PER vs. (Es/N0) curves. • The resulting PER values can be used to determine actual system throughput. Batra and Shoemake, Texas Instruments

  3. Assumptions • Complex additive white Gaussian noise: • Thermal noise floor = -114 dBm/MHz. • Matched-filter receiver architecture. • 802.15.2 Path Loss Model [802.15/138r0]. • Same transmit power for all modulation schemes. • Same implementation loss and noise figure for all receivers. Batra and Shoemake, Texas Instruments

  4. n(t) g*(-t) s(t) r(t) y(t) g(t) Ak t = kT + (Es/N0) for CCK/PBCC • Initially, assume no path loss. Let g(t) be a unit-energy pulse. • After the sampler, the received signal is: • Received signal and noise power: E[|A0|2] = TstPs and s2 = N0.  (Es/N0)CCK/PBCC = TstPs/N0, where Ps is the received power and Tst = 1/(11 MHz). Batra and Shoemake, Texas Instruments

  5. y0(t) n(t) Ak,0 Ak,1 s(t) r(t) g1(t) g0(t) g0(t) g1(t) yN-1(t) Ak,N-1 t = kT y1(t) + + gN-1(t) gN-1(t) (Es/N0) for 802.11a/CCK-OFDM • Initially, assume no path loss. Let gn(t) be orthonormal pulses. • After the mth sampler, the received signal is: • Received signal and noise power: E[|A0,m|2] = TmtPs/N and s2 = N0.  (Es/N0)802.11a/CCK-OFDM = (TmtPs/N)/N0, where N is the # of sub-carriers, Ps is received power, and Tmt = 3.2ms. Batra and Shoemake, Texas Instruments

  6. Summary of (Es/N0) • For CCK/PBCC, the received (Es/N0) is given by: (Es/N0)CCK/PBCC = TstPs/N0, where Tst = 1/(11 MHz). • For 802.11a/CCK-OFDM, the received (Es/N0) is given by: (Es/N0)802.11a/CCK-OFDM = (TmtPs/N)/N0, where N = 52 (# of used sub-carriers) and Tmt = 3.2ms. • Note that the gap between CCK/PBCC & 802.11a/CCK-OFDM is: Gap = (Es/N0)CCK/PBCC/ (Es/N0)802.11a/CCK-OFDM = 1.6946 dB Batra and Shoemake, Texas Instruments

  7. IEEE 802.15.2 Path Loss Model • For distances less than 8m, we assume LOS: Lpathloss = 20log10( 4pr/l) r 8m, • For greater than 8m, we assume a path loss exponent of 3.3: Lpathloss = 58.287 + 33log10(r/8) r > 8m, where r = range in meters and l = wavelength in meters. • Note that at a frequency of 2.45 GHz, l = 0.1224m. Batra and Shoemake, Texas Instruments

  8. Other Losses • To obtain a realistic range versus rate comparison, we must include other losses seen by the receiver. • Examples of other losses include: • Noise figure for the front-end of the receiver • Implementation loss • Margin for multipath • We assume that the receiver has an overall loss of: Lotherloss = Lnoisefigure + Limplementation + Lmultipath = 16 dB Batra and Shoemake, Texas Instruments

  9. Calculation of Received(Es/N0) • The received (Es/N0) for CCK/PBCCis therefore given by: (Es/N0)RX,CCK/PBCC = (Es/N0)CCK/PBCC – Lpathloss – Lotherloss • Similarly, the received (Es/N0) for 802.11a/CCK-OFDMis given by: (Es/N0)RX, 802.11a/CCK-OFDM = (Es/N0)802.11a/CCK-OFDM – Lpathloss – Lotherloss Batra and Shoemake, Texas Instruments

  10. Calculation of Throughput • Assumptions: • IEEE 802.11b short preamble • A data length = 1000B • ACK packets are transmitted • No backoff (only a DIFS is included; similar to 802.11e HCF) • Maximum Sustainable Throughputs (MST) can be found in doc. 01/059 by Halford, Webster and Zyren. • For a given PER, the actual throughput can be found by dividing the MST by the average number of attempts it takes to successfully transmit a packet, i.e., Batra and Shoemake, Texas Instruments

  11. PER vs. SNR for CCK/PBCC Batra and Shoemake, Texas Instruments

  12. PER vs. SNR for 802.11a/CCK-OFDM Batra and Shoemake, Texas Instruments

  13. Range vs. Rate Batra and Shoemake, Texas Instruments

  14. Range vs. Rate for PER = 10-2 (1) * Range is normalized with respect to CCK11 Batra and Shoemake, Texas Instruments

  15. Range vs. Rate for PER = 10-2 (2) Batra and Shoemake, Texas Instruments

  16. Conclusions • For similar data rates, PBCC can cover a much larger range than either CCK, 802.11a-OFDM, or CCK-OFDM. • The throughput for 802.11a-OFDM is much larger than that of CCK-OFDM for the same range. • The reason that 802.11a-OFDM has a larger throughput than PBCC is because the 802.11a-OFDM preamble is muchshorter than the 802.11b short preamble. Batra and Shoemake, Texas Instruments

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