1. IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 63, NO. 5, JUNE 2014
Resolving the Unfairness of Distributed Rate Control in the IEEE WAVE Safety Messaging
Byungjo Kim, Member, IEEE, Inhye Kang, Member, IEEE, and Hyogon Kim, Member, IEEE

2. WAVE(Wireless Access in Vehicular Environment) 개요
IEEE p
IEEE p의 PHY는 5GHz 대역에서 동작하는 IEEE a PHY로부터 최소한의 변경만을 고려
OFDM (Orthogonal Frequency Division Multiplexing) 20MHz 대역폭 대신 10MHz 대역폭을 이용
IEEE p system
Data rate : 3, 4.5 Mbps (BPSK), 6, 9 Mbps (QPSK), 12, 18 Mbps (16QAM), 24, 27 Mbps (64QAM)
Bandwidth : 10 MHz
Channel Switching : Interval 100 ms (CCH/SCH 50 ms, guard time 10 ms)
Throughput : 1.0Mbps (IEEE p, data rate 3 Mbps)
Coverage : 500 m ~ 1000 m (V2V,V2I), 1000m (I2I, IEEE g)
Vehicle Velocity : 160 km/h

3. WAVE(Wireless Access in Vehicular Environment) 개요
IEEE p +IEEE 1609
고속으로 주행하는 차량 환경에서 통신서비스를 제공하기 위하여 특화된 차세대 ITS 통신 기술
WLAN 기술을 기반으로 자동차 환경에 맞도록 수정
DSRC (Dedicated Short Range Communication) 기술의 일종
V2I (Vehicle-to-Infrastructure)과 V2V(Vehicle-to-Vehicle) 통신을 지원

4. WAVE(Wireless Access in Vehicular Environment) 개요
IEEE 1609
IEEE Architecture
IEEE Remote management service
IEEE Security
IEEE Networking services
IEEE Multi-channel operation

5. Safety Communication in WAVE
The WAVE standard allocates seven 10-MHz channels in a 5.9-GHz band for communication between WAVE devices such as on-board unit (OBU) and road-side unit.
The frequency band is often called the dedicated short-range communication (DSRC) band.
Unlike in wireless LAN, WAVE communica-tion can use two channel. The central channel among the seven, called the control channel (CCH), is exclusively used by vehicular safety messages (e.g., BSM) and service announcements, and the services provided in the remaining six channels are called service channels.

6. Problem
Most congestion control proposals in the IEEE WAVE context aim at regulating the BSM transmission rate in order to not exceed a certain channel utilization threshold.
What these proposals have failed to grasp, however, is that individual rate settings of even closely neighboring vehicles can dramatically diverge
Such pathology has a negative implication on the levels of awareness they will offer to ambient vehicles, raising a safety issue.

7. A. Threshold-Based Control
In order not to diffuse the focus, we employ the simplest adaptation mechanism in this paper, which is the additive-increase multiplicative-decrease (AIMD).
(a) Adjusted rate. (b) CBP.

8. Hysteresis-Based Control
(a) Adjusted rate. (b) CBP.

9. ETSI-Style Rate Control
Decentralized congestion control (DCC) algorithm : employs a state machine with three states. These state assign different power, messaging rate, channel sensitivity PHY transmission mode.
In the ETSI specification, the rate increase decision is made when the given condition on CBP holds for 5s(= NDL_timeUp). Likewise, the rate decrease is made when the required condition holds for 1 s (= NDL_timeDown)

10. ETSI-Style Rate Control
We notice that the unfairness in the rate setting is severe among neighboring vehicles.
Still, the CBP, as shown in Fig., does not show correspondingly wild deviations although it shows some differences.
(a) Adjusted rate. (b) CBP.

11. Mean-Checked Threshold-Based Control
The rate assignments in one’s neighborhood N are additionally considered before the rate assignment is made (i.e., lines 4 and 8).
The neighborhood is defined by the vehicles in one’s communication range, i.e., N = {v1,v2,...,vn}

12. Mean-Checked Threshold-Based Control
It successfully finds the rate equilibrium for neighboring vehicles while maintaining the target channel utilization.
(a) Adjusted rate. (b) CBP.