Considerations about Wideband Data Transmission at 4.9 GHz for an hypothetical city wide deployment

Transcription

1 Considerations about Wideband Data Transmission at 4.9 GHz for an hypothetical city wide deployment Leonhard Korowajczuk CEO, CelPlan Technologies, Inc. WCA Public Safety Task Force 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 1

2 Wideband Data Transmission Multi-path delay is a major impairment in data transmission Several techniques exist that mitigate its impact, as long as the delay is smaller than 1 data bit Large data rates shrink the allowed multi-path delay to impractical numbers Data Rate (Mbit/s) bit delay (ns) Distance (m) OFDM solves this issue by splitting the data between subcarriers, diminishing the data rate per sub-carrier WI-FI (802.11a) uses 64 sub-carriers, while WIMAX (802.16) will use up to 1024 sub-carriers 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 2

3 Wi-Fi Characteristics Wi-Fi is becoming the world standard for real wideband data transmission WiMAX is the natural evolution of Wi-Fi Wi-Fi equipments can be made WiMAX ready Ideally 4.9 GHz should use COTS parts to benefit from the mass produced low cost of Wi-Fi Wi-Fi uses 64 sub-carriers (312. Khz spacing) Carrier 0 is null Carriers 1 to 26 used for data Carriers 27 to 31 are not used Parameters considered Receiver Noise Figure= 6 db 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 3

4 COTS Technology There are two main vendors of Wi-Fi chips and its functional software Atheros: AR002 to AR006 Conexant: PRISM GT/ PRISM World Radio Both vendors support 4.9 GHz settings Atheros supports 20/10/ MHz Conexant supports 20 MHz, with 10 MHz planned Chips MAC (Medium Access Control) Baseband processor Radio System on a chip 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 4

5 Wi-Fi Protocol The existing protocol is highly inefficient for small packets The access procedure implies in large wait times, in which no data is sent data wait ime data wait time da ta wait time Gross data rate 9 Mbit/s Packet data bytes bit us MAC data bit us ACK data bit us Total data us Total wait time (DIFS, PHY, SIFS, propagation) us Total duration of packet us Overhead 39788% 622% 311% 1% 78% 39% 19% 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information

6 Wi-Fi Software Adaptations for Mobile Public Safety Solutions Packet aggregation Small packets are aggregated before transmission Optimized Access strategy Overcomes hidden node and back off issues Bandwidth and QOS management Bandwidth and delay are managed to provide fair access Mobile routing Grid routing System Access restriction Centralized Authentication management Encryption Options Network Management 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 6

7 Multi-path Delay in WI-FI M ultipath Constraints Multipath Delay Spread (ns) Multipath Delay Spread (ns) Delay spread distance (m) Delay Spread Distance (m) Bandw idth (MHz) 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 7

8 20 MHz OFDM Parameters with 64 sub-carriers 20 Mhz OFDM parameters with 64 sub-carriers Required S/N (db), Gross Data Rate (Mbit/s) Required SNR (db) Gross Data Rate (Mbps) Receive Sensitivity (dbm) BPSK 1/2 BPSK 1/2 BPSK 1/2 BPSK 1/2 BPSK 1/2 QPSK 1/2 QPSK 1/2 QPSK 3/4 16 QAM 1/216 QAM 3/464 QAM 2/364 QAM 3/ Receive Sensitivity (dbm) Selected Modulation Scheme 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 8

9 10 MHz OFDM Parameters with 64 sub-carriers 10 MHz OFDM parameters with 64 sub-carriers Required S/N (db), Data Rate (Mbit/s) Required SNR (db) Gross Data Rate (Mbps) Receive Sensitivity (dbm) BPSK 1/2 BPSK 1/2 BPSK 1/2 QPSK 1/2 QPSK 3/4 16 QAM 1/2 16 QAM 3/4 64 QAM 2/3 64 QAM 3/ Receive Sensitivity (dbm) Selected Modulation Scheme /18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 9

10 MHz OFDM Parameters with 64 sub-carriers M Hz OFDM parameters with 64 sub-carriers Required SNR (db) Gross Data Rate (Mbps) Receive Sensitivity (dbm) Required S/N (db), Data Rate (Mbit/s) Receive Sensitivity (dbm) BPSK 1/2 BPSK 1/2 BPSK 1/2 QPSK 1/2 16 QAM 1/2 16 QAM 3/4 64 QAM 2/ Selected Modulation Schem e 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 10

11 1 MHz OFDM Parameters with 64 sub-carriers 1 M Hz OFDM parameters with 64 sub-carriers Required SNR (db) Required S/N (db), Data Rtae (Mbit/s) Theoretical Data Rate (Mbps) Receive Sensitivity (dbm) Receive Sensitivity (dbm) BPSK 1/2 16 QAM 1/2 16 QAM 3/ Selected Modulation Schem e 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 11

12 Theoretical C/I for different channel reuse A minimum number of channels is required to achieve desired C/I This number of channels depends of the path loss slope The calculations below apply to regular cells on regular terrain, placed on street corners Practical systems require additional margins Number of channels Reuse Distance (cell radius) Path Loss Slope C/I /18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 12

13 Theoretical availability at cell edge S/N required for 9 Mbit/s with 8 MHz bandwidth= 12. db Slow fading standard deviation= 4 db user-user (worst case) RAN-user RAN-RAN, user-user (best case) Number of Channels Reuse distance (in radius) Slope (db/dec) Theoretical availability at edge 38% 91% 99% 100% 100% 100% 29 34% 88% 99% 100% 100% 100% 28 % 8% 98% 99% 100% 100% 27 26% 80% 97% 99% 99% 100% 26 22% 7% 9% 98% 99% 100% 2 19% 69% 92% 96% 98% 99% 24 16% 63% 88% 94% 97% 98% 23 13% 6% 84% 91% 9% 97% 22 11% 49% 78% 86% 92% 9% 21 9% 42% 71% 81% 87% 92% 20 7% 3% 64% 74% 81% 87% 19 % 29% 6% 66% 74% 81% 18 4% 23% 47% 7% 66% 73% 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 13

14 Link Budget Low power and High power transmitters are considered Omni antennas are used for local cells Directional antennas are used for backhaul 10 MHz, 9 Mbps 10 MHz, 6 Mbps 10 MHz, 1 Mbps omni directional omni directional omni directional Transmit power (dbm) TX Cable losses (db) TX Antenna gain (dbi) RX Antenna gain (dbi) RX Cable losses (db) Receiver Sensitivity Shadow/ Interference Margin Path Loss /18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 14

15 Propagation at 4.9 GHz Measurements done in NYC Measurements done with LOS or near LOS Multi path limited to few hundred meters Predictions done using CelPlan Microcell model Prediction mean square error around. db compared to measurement Average slow fading of 3 db (for a 12 m grid) Shadow fading (obstruction loss) very severe Tree 8 db Car 10 db Minimum recommended margin of 10 db Average path loss slope measured 18 db/ decade in canyon areas with no trees (better than free space due to canyon effect) Up to db/decade in residential and highly treed areas Measurement standard deviation of 4.43 db ( m pixel) Antenna diversity suggested at the transmitter and receiver (MIMO) 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 1

16 Comparing measurements with predictions Minimum of 2 samples per grid, Grid Size = 1 m Location Std Deviation Grid Accepted Grids 90% 9% 99% 6 th Av with 38St Greenwich with Warren Central Park with th Avenue Brooklyn Minimum of 2 samples per grid, Grid Size = m Location Std Deviation Grid Accepted Grids 90% 9% 99% 6 th Av with 38St Greenwich with Warren Central Park with th Avenue Brooklyn /18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 16

17 Prediction Accuracy compared to measurements 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 17

18 Path Loss at 4.9 GHz Slope (db/decade) Distance (km) /18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 18

19 4.9 GHz Propagation in Urban Environments Under canopy and over vehicle tunnel propagation is most effective Antenna diversity is strongly recommended Antenna positioning should be carefully planned to avoid obstructions and benefit from reflections 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 19

20 Interference cases for urban street RAN to User coverage Average distance of 9 cell radii (using channels) 0% interference probability RAN 1 RAN 2 Er Ed User to RAN Average distance of 9 cell radii (using channels) 0% interference probability from each source (up to 4 directions) RAN 1 RAN 2 Er Ed 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 20

21 Interference cases for urban street RAN to RAN coverage Average distance of 10 cell radii (using channels) Interference probabilities: 1 source= 2%, 2 sources= 37.%, 3 sources-2%, 4 sources= 6.7% (one from each direction) RAN 1 RAN 2 Er Ed User to User Average distance of 8 or 10 cell radii (using channels) 2% interference probability from 8 cell radius and 2% from10 cell radius RAN 1 RAN 2 Er Ed 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 21

22 Emission Mask FCC in its MO&O of November 9, 2004 adopted the following solution for the emission mask DSRC-A mask for emissions up to 20 dbm DSRC-C mask for emissions above 20 dbm This makes an inefficient use of spectrum Higher power is required to space the cells by at least a block Too much guard band is enforced to comply with the mask using COTS equipment Filter solution does not apply as existing chips do not provide access to IF or are zero IF CelPlan plans to file a petition for reconsideration with the FCC as soon as the first field tests are done 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 22

23 DSRC-A Emission Mask (802.11a) 4.9 GHz emission and mask DSRC-A ( A) M Hz 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 23

24 4.9 GHz a Emission 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 24

25 DSRC-A Emission Mask (802.11a 10 MHz) 4.9 GHz emission and mask DSRC-A (802.11A ) -20 M easur ements hi gher hal f of spectr um M easur ements l ower hal f of spectr um M Hz 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 2

26 Original L Mask (10 MHz) 4.9 GHz emissio n and mask DSRC-A (802.11A) 4.9 GHz M easur ements hi gher hal f of spect r um M easur ements l ower hal f of spectr um M Hz 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 26

27 DSCR-C Mask (10 MHz) 4.9 GHz emission and mask DSRC-A (802.11A ) 4.9 GHz DSRC-C M easur ements hi gher hal f of spectr um M easur ements l ower hal f of spectr um M Hz 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 27

28 18 MHz DSCR-C Mask with 10 MHz a emission 4.9 GHz e m is s ion and m as k D SR C -C M e as ur ement s hi gh er hal f of s pe c t r um M e as ur ement s l ow er hal f of s pec t r um db M Hz 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 28

29 Channel Plan The Channel Plan below accommodates the emission mask, but adds restrictions and makes plan more difficult, but it is compatible with an eventual mask change Channel 1 (4.94 GHz): 20 dbm 10 MHz Channel 2 (4.9 GHz): dbm 18 MHz Channel 3 (4.96 GHz): dbm 18 MHz Channel 4 (4.97 GHz): dbm 18 MHz Channel (4.98 GHz): 20 dbm 10 MHz Additional low power channels can be added for PANs with MHz and 1 MHz bandwidth to be used with palmtops and portable equipment The PANs will select the best available channels in each cell 10 x MHz channels start at GHz: 20 dbm max 0 x 1 MHz channels start at GHz: 20 dbm max 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 29

30 Channel Plan 4.9 GHz Channel Plan T ran sm it P o w er (dbm ) channel 1 channel 2 channel 3 channel 4 channel Frequency (MHz) 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information

31 Network Layout Mobile Clients Wireless Access Point that interconnects the client applications (video, voice, text, control and command) RAN (Radio Access Node) Wireless Access Node (cell) that communicates with its mobile clients and routes information to and from the local backhaul node Backhaul Wireless and Wireline interconnection from the RAN to the Operations Center The Wireless Backhaul is divided in zones that have access to the Wired Backhaul Wireless Backhaul nodes are co-located with RANs and use directional antennas to interconnect between themselves in a grid pattern The Router function chooses the best routing in the grid, to balance traffic and minimize number of hops Each hop increases the transmission latency as data must be retransmitted 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 31

32 Latency calculations Number of users Channel bit rate Mbit/s Packet size bytes Effective bidirectional data rate Mbit/s Effective downstream only data rate Mbit/s Effective upstream only data rate Mbit/s effective packet duration bidirectional ms effective packet duration downstream ms effective packet duration upstream ms effective throughput per user bidirectional Mbit/s effective throughput per user downstream Mbit/s effective throughput per user upstream Mbit/s average latency bidirectional ms average latency downstream ms average latency upstream ms 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 32

33 Latency and Hops Voice quality at different delays (VoIP) < 10 ms 10 to 0 ms >0 ms design objective good acceptable bad 10 ms Number of users Maximum number of RAN hops for bidirectional hops Maximum number of RAN hops for downstream hops Maximum number of RAN hops for upstream hops Maximum regular zone size for bidirectional RAN Maximum regular zone size for downstream RAN Maximum regular zone size for upstream RAN 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 33

34 Mobile Handoff Mobile client registration function allows routing to direct data to/from mobile client Changes are required in IP procedures Minimum time in a cell: > 2.6 s (140 km/h in a 0 m cell) Association and disassociation process: < 00ms Several strategies allow diminish this time Enough to transmit 1000 packets of 12 bits Effective data rate will drop during handoff periods 11/18/2004 Copyright CelPlan Technologies, Inc.- Proprietary Information 34