Method for determining data rate and packet length in mobile wireless networks
A method is provided to determine optimal data rate and packet length in mobile networks. The method directly determines the optimal packet length (L) and data rate (D), which allows fast convergence in the mobile channel. The method automatically identifies and quantifies channel conditions, as well as adjusts parameters according to changes of channel conditions. A variable (Channel condition Index (CCI)) is abstracted from simulations and then used to describe and quantify the impact of three components of channel conditions: signal-to-noise ratio (SNR), multipath environment and velocity. Based on packet completion rate (PCR) status, the channel condition is identified in terms of CCI value. Once CCI is identified, the model of effective throughput G is directly optimized to locate the best packet length (L) and data rate (D).
1. A method for determining a data rate and a packet length for a data transmission in a wireless communication network, the method comprising:
operating a wireless communication device within the wireless communication network to:
initialize a starting value for a packet length and a data rate;
determine an effective throughput (G) based on a measured value of a packet completion rate (PCR);
determine a channel condition index based on the determined effective throughput;
adjust the packet length based on the determined channel condition index;
adjust the data rate based on the determined packet length; and
transmit at least one data transmission using the adjusted packet length and the adjusted data rate; and
wherein determining the channel condition index further comprises:
calculating the channel condition index based on the current data rate;
identifying the effective throughput (G) as a function of packet length (L) and the channel condition index (CCI); and
finding a value of the channel condition index for which the function has the closest value to the effective throughput (G).
2. The method of claim 1 , wherein the wireless communication device utilizes modeling techniques to determine an optimal packet length and an optimal data rate for the adjusted packet length and the adjusted data rate.
3. The method of claim 1 , wherein the operation of determining the effective throughput (G) based on a measured value of a packet completion rate (PCR) comprises calculating the effective throughput by:
G
=
L
·
N
·
pcr
t
sd
+
t
sc
+
t
e
where:
L is a packet length in orthogonal frequency-division multiplexing (OFDM) symbols,
N is a number of bytes per symbol, whose value is determined based on modulation.
PCR is a packet completion rate,
T sd is a transmission time for data packets,
T sc is a transmission time for control packets, and
T e is a constant which summarizes a processing delay.
4. The method of claim 1 , wherein the channel condition index comprises an abstract variable which is an estimation based on one or more simulations.
5. The method of claim 4 , wherein the channel condition index quantifies one or more channel conditions considering one or more of a signal-to-noise ratio (SNR), a multipath environment, and a velocity.
6. The method of claim 1 , wherein the effective throughput function is expressed by an empirical rational expression of:
G
=
g
(
β
,
L
)
=
p
0
+
0.1
p
1
L
+
0.01
p
2
L
2
+
0.0001
p
3
L
4
1
+
p
4
β
+
p
5
β
2
+
p
6
β
4
*
1
1
+
p
7
β
+
0.1
p
g
L
+
0.01
p
9
L
2
where:
β is the channel condition index,
L is a packet length in orthogonal frequency-division multiplexing (OFDM) symbols, and
p 0 through p 9 are constants which are obtained by applying curve fitting techniques.
7. The method of claim 1 , wherein the operation of determining the channel condition index comprises operating the wireless communication device to:
store, in a memory of the wireless communication device, a table of effective throughput as a function of channel condition index and packet length for each data rate; and
obtain the channel condition index through looking up in the table.
8. The method of claim 1 , wherein the operation of adjusting the packet length (L) comprises operating the wireless communication device to:
calculate the packet length (L) using the obtained channel condition index and g D by finding the packet length value (L) for which:
∂
g
D
(
L
)
∂
L
=
0
,
where:
g D is an expression of effective throughput for a data rate (D), and
∂ is the partial derivative function.
9. The method of claim 1 , wherein the operation of adjusting the packet length (L) comprises operating the wireless communication device to:
store, in a memory of the wireless communication device, a table of the values of the packet length (L) for which the function
∂
g
D
(
L
)
∂
L
=
0
has a maximum value; and
obtain the value of packet length from the table.
10. The method of claim 1 , wherein the operation of adjusting the data rate comprises operating the wireless communication device to:
identify an optimal packet length (L) for each data rate;
obtain the corresponding effective throughput g D , value for each of the optimal packet lengths (L); and
select a date rate that corresponds with a maximum corresponding effective throughput g D value.
11. The method of claim 1 , further comprising operating the wireless communication device to:
change a stored packet completion rate (PCR) value based on one or more PCR statistics obtained from a current packet transmission.
12. The method of claim 11 , further comprising operating the wireless communication device to:
repeat the operations of determining the channel condition index; the adjusted packet length; and the adjusted data rate; and
transmit at least one data transmission using the adjusted packet length and the adjusted data rate.
13. A wireless communication device comprising:
a processor that is configured to:
initialize a starting value for a packet length and a data rate;
determine an effective throughput (G) based on a measured value of a packet completion rate (PCR);
determine a channel condition index based on the determined effective throughput;
adjust the packet length based on the determined channel condition index;
adjust the data rate based on the determined packet length;
transmit at least one data transmission using the adjusted packet length and the adjusted data rate; and
wherein the processor is configured to determine the channel condition index by:
calculating the channel condition index based on the current data rate;
identifying the effective throughput (G) as a function of packet length (L) and the channel condition index (CCI); and
finding a value of the channel condition index for which the function has the closest value to the effective throughput (G).
14. The wireless communication device of claim 13 , wherein the processor is configured to adjust the data rate by:
identifying an optimal packet length (L) for each data rate;
obtaining the corresponding effective throughput g D value for each of the optimal packet lengths (L); and
selecting a date rate that corresponds with a maximum corresponding effective throughput g D value.
15. The wireless communication device of claim 13 , further comprising a memory that stores a table of effective throughput as a function of channel condition index and packet length for each data rate and wherein the processor is configured to obtain the channel condition index through looking up in the table.
16. A method for determining a data rate and a packet length for a data transmission in a wireless communication network, the method comprising:
operating a wireless communication device within the wireless communication network to:
initialize a starting value for a packet length and a data rate;
determine an effective throughput (G) based on a measured value of a packet completion rate (PCR);
determine a channel condition index based on the determined effective throughput;
adjust the packet length based on the determined channel condition index;
adjust the data rate based on the determined packet length;
transmit at least one data transmission using the adjusted packet length and the adjusted data rate; and
wherein determining the channel condition index comprises:
storing, in a memory of the wireless communication device, a table of effective throughput as a function of channel condition index and packet length for each data rate; and
using the table to determine the channel condition index.