1 Introduction
-
A novel interference-aware high-throughput channel allocation mechanism, HT-CAM, has been proposed.
-
Interference-free maximum independent sets of link-band pairs have been constructed exploiting conflict graphs so as to maximize the spatial reusability of licensed channels.
-
A mixed-integer linear programming (MILP) optimization function is formulated which maximizes network throughput while maintaining QoS requirements of vehicular applications in terms of channel bandwidth and data delivery delay.
-
The performance of HT-CAM is simulated extensively and compared with the state-of-the-art channel allocation mechanisms using NS-3.
2 Related works
3 System model and assumptions
Notation | Description |
---|---|
B
| Set of licensed channels in the network |
W
b
| Bandwidth of channel b
|
Set of OBUs registered with an RSU | |
B
i
| Set of available licensed channels at OBU i
|
B
ij
|
B
i
∩B
j
, set of common channels available at i and j
|
T
| Length of scheduling cycle |
N
i
| Set of neighbors of OBU i
|
\(P_{i}^{tr}\)
| Transmission power of an OBU i
|
D
ij
| Number of data packets awaited in the queue of OBU i for transmission from OBU i to OBU j
|
ψ
ij
| Required data rate for transmission |
δ
ij
| Tolerable maximum transmission delay |
Z
b
| PU idle time at channel b
|
λ
b
| PU arrival rate at channel b
|
\(q_{\textit {ij}}^{b}\)
| Transmission quota of OBU pair {i,j} on channel b
|
\(s_{\textit {ij}}^{b}\)
| Success probability of OBU pair {i,j} on channel b
|
\(R_{\textit {ij}}^{b}\)
| Achievable data rate from OBU i to OBU j on channel b
|
ζ
| Medium access delay |
\(\text {SINR}_{\textit {ij}}^{b}\)
| SINR value between OBU i and OBU j on channel b
|
L
i
| Length of the packets at the transmission queue of OBU i
|
\(\tau _{\textit {ij}}^{b}\)
| Required tx time for OBU pair {i,j} on channel b
|
ρ
I
| Weight of independent set I
|
Θ
| Set of all maximum independent sets |
Set of all OBU pairs requesting transmission | |
Set of OBUs in the interference range of OBU i
| |
ω(G) | Set of all independent vertices in a conflict graph G
|
4 Design of HT-CAM
4.1 Activities of OBUs
4.1.1 Neighbor discovery
4.1.2 PU traffic pattern prediction
4.1.3 Transmission request
4.2 Activities of RSU
4.2.1 Computation of λ b and Z b
4.2.2 Derivation of Q ij and S ij
4.2.3 Generation of independent sets
-
Condition 1: Two different OBU pairs have at least one common OBU, that is, {i 1,j 1}∩{i 2,j 2}≠∅
-
Condition 2: If two OBU pairs are using the same channel, their transmissions interfere with each other when the transmitter or receiver OBU of one pair falls within the interference range of the transmitter or receiver OBU of the other pair. That is, if there are two channel assignments (i 1 j 1,b 1) and (i 2 j 2,b 2) such that b 1=b 2, then the transmissions of OBU pairs (i 1 j 1,b 1) and (i 2 j 2,b 2) interfere iff or and vice versa. Here, is the set of OBUs that fall within the interference range of OBU i.
4.2.4 High-throughput channel allocation
5 Performance evaluation
5.1 Simulation environment
Parameter | Value |
---|---|
Number of vehicles | 12∼40 |
Number of PU | 3∼24 |
Number of channels | 3∼10 |
Channel bit rate | 6 Mbps |
Data packet size | 1024 bytes |
ACK size | 14 bytes |
Control packet size | 16 bytes |
Channel bit error rate | 10−3
|
Vehicles speed | 36∼90 km/h |
Vehicle transmission range | 100 m |
RSU transmission range | 400 m |
MAC layer model | AdhocWifiMac model |
Physical layer model | YansWifi model |
Length of road segment | 1000 m |
Simulation time | 500 s |
5.2 Performance metrics
-
Throughput: The number of bytes received successfully by each destination node per unit time is measured, and then the average is taken for all destinations to calculate the average throughput achievable by a channel allocation mechanism. Higher value corresponds to better performance.
-
Packet delivery ratio: It is the ratio of total number of packets successfully delivered at destination nodes to the total number of packets generated during the whole simulation period.
-
Channel utilization ratio: It is the ratio of the number of scheduled OBU pairs to the number of available licensed channels during the whole simulation period.
-
End-to-end average packet delivery delay: The end-to-end delay is the time from when a packet becomes head of the line packet to the time when the source receives acknowledgement from the destination for that packet. Then, the average delay is calculated for all packets sent during the whole simulation period. Lower end-to-end delay means better channel allocation mechanism.
-
Operation overhead: We calculate the amount of control bytes transmitted during the whole simulation period for successful transmission of each byte of user data in the studied channel allocation mechanisms to compare the operation overhead.