Performance Evaluation of Inter-vehicle Packet Relay for Fast Mobile Road-vehicle Communication Ryoichi SHINKUMA Visiting scholar, WINLAB, Rutgers Assistant professor, Kyoto University, Japan *Takayuki YAMADA, and Tatsuro TAKAHASHI Kyoto University * Presently, with NTT Network Innovation Laboratories.
Outline • Background & goal • Problems of road-vehicle communication in fast mobile environments • Our inter-vehicle packet relay technique • Simulation results • Conclusion 2
Background & goal Background: • Road-vehicle communication on highways –Applications: safety services, location-aware services, content delivery etc –Requirements: AP • High throughput • Wide communication coverage Goal: • To satisfy the above requirements 3
Problems of road-vehicle communication in fast mobile environments • Mobile stations (MSs) have to connect to fixed roadside access points (APs). • Large relative speed between MSs and APs causes ... 1.Time-varying fading caused by large Doppler shift 2.Wide dynamic range of path loss AP 3.Short period of being within coverage of an AP 4
Problems of IEEE802.11a WLAN in fast mobile environments Max. transmission rate [Mbps] IEEE802.11a,1500 Bytes Long frame 60 0 km/h 20 km/h transmission 50 40 km/h 60 km/h ���� 80 km/h 40 100 km/h 120 km/h Time-varying fading 30 by Doppler shift 20 10 Not correctly 0 0 10 20 30 40 compensated ! E b / N 0 [dB] Rx power As moving speed fading increases, transmission rate decreases Time 5 One frame duration
Proposed method: Inter-vehicle packet relay technique Receiving packets via other, slower vehicles Relative speed per hop Channel-quality decreases improvement => V MS > V RS >> (V MS -V RS ) Increased throughput – Reducing Doppler shift and coverage – Reducing dynamic range of path loss RS: Relay Station AP V RS RS MS MS 6 V MS V MS
Simulation parameters IEEE802.11a WLAN Parameters Frequency band 5GHz Moving speed of MS/RS 100 / 80 km/h Data length 1500 Bytes RS interval (crowded and not) 100 / 400 m Transmission power 12 dBm AP interval 100 ~ 2000 m Noise figure 10 dB AP / vehicle height 6 / 1.5 m μ sec 96 Overhead per frame Lane width 3.5 m Overhead for handover 100 msec Route selection phase 5 msec AP2 AP1 AP3 Lane 1 V RS (RSs) Lane 2 p 23 p 12 V MS (MS) 7
Simulation model • The observed MS ran from P 1 to P 2 , adaptively choosing a communication route that maximizes the throughput from an AP to the MS (including direct route from AP) • RSs ran with constant speed and equal intervals. AP1 AP3 100~2000m AP2 100/400 m Lane 1 V RS =80km/h (RSs) Lane 2 p 1 p 2 V MS =100km/h (MS) 8 Choice!
Geometric propagation model AP Received signal= + a direct path + a road reflection path + several delay paths Sharply fluctuated -40 2 paths + 3 delay paths 2 paths -60 Loss [dB] ITU-R LoS lower bound -80 Free space -100 -120 -140 0 200 400 600 800 1000 9 (AP) Position [m]
Simulation result: connected time (coverage metric) Normalized by conventional method only using direct route 2 Normalized connected time D RS = 100 [m] • Time during D RS = 400 [m] which frame 1.8 success rate of the MS exceeds 36 sec 5% 1.6 • Frame success 33 sec rates of both 1.4 links of two-hop routes have to be over 5% 1.2 22 sec 1 0 100 250 500 1000 1500 2000 AP interval [m] Conventional method D RS : RS interval 10 Increased communication coverage
Simulation result: average throughput (quality metric) Normalized by conventional method only using direct route θ AV is • Average throughput given by 1.8 D RS =100m Normalized throughput D RS =400m 1 Nl ∫ D θ = RS dx . ( ) ( ) − AV D t p t p 0 1.6 RS 23 12 2.8 Mbps – All possible default positions of RSs are 1.4 considered t(p) : time when MS 2.2 Mbps is at position p 1.2 D RS : RS interval N : number of 1.9 Mbps success frames 1 l : data length 0 100 250 500 1000 1500 2000 AP interval [m] Conventional method 11 Increased average throughput
Conclusion • Inter-vehicle packet relay technique for road- vehicle communication in fast mobile environment Reducing relative speed – Improved channel quality – Increased throughput and communication coverage • Future work – Testing our method in multi-user environment • MAC • Route selection algorithm [IEEE Globecom06, IEICE Trans vol.E90-B no.9, IEEE CCNC08] 12
13 Thank you for your attention.
Problems in multiple access environment What problems are caused? � Frame collision � Interference � Solutions to avoid the frame collision are [Between neighboring areas] – To assign different channels to neighboring areas [Within coverage of a single AP] – To use point coordination function (PCF) – To limit number of hops to two � But … there is still an interference problem. 14
Interference problem • Comparison with conventional method – Additional interference by RSs between neighboring areas • Features of our method – Seldom choosing the RSs near the border and far from AP due to low transmission rate – Ability to shorten MSs' transmission time per frame by choosing RS-MS links of high transmission rate Here, seldom chosen Overlapped zone due to low transmission rate Uplink Ch1 AP1 AP2 Lane 1 (RS’s lane) Lane 2 Ch2 (MS’s lane) Area of interference Transmission rate of RS-MS links are Shorter than the Direct 15 with neighboring channel higher than that of the direct link
Evaluation results : Interference between neighboring areas Overlapped Normalized by conventional Normalized total transmission time zone method only using direct route AP interval: 1000 m 1 D RS =100 m Transmission time [sec] D RS =100m D RS =400 m D RS =400m 1.2 Direct only 0.8 0.6 1 0.4 0.8 0.2 0 0.6 0 100 200 300 400 500 0 100 250 500 1000 1500 2000 (AP) (border) AP interval [m] Position [m] Total transmission time of MS and RSs at Total transmission time each position in overlapped zone Our method does not cause additional 16 interference between neighboring areas.
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