KR20130119667A - Method of operating terminals and access point to maximize energy efficiency of wireless local area network - Google Patents

Abstract

A method for operating terminals and access points to maximize the energy efficiency of a wireless local area network is disclosed. The present invention provides a technology to maximize energy efficiency for the entire wireless local area network by determining transmission power and transmission mode in the light of the energy consumption of terminals which communicate with access points in the wireless local area network and remaining terminals. [Reference numerals] (AA) Start;(BB) End;(S200) Step for determining transmitting power and a transmitting mode;(S210) Step for determining the processing amount of WLAN;(S220) Step for calculating the amount of WLAN energy consumption per unit hour;(S230) Step for calculating WLAN energy efficiency;(S240) Step for determining transmitting power and a transmitting mode

Description

METHOD OF OPERATING TERMINALS AND ACCESS POINT TO MAXIMIZE ENERGY EFFICIENCY OF WIRELESS LOCAL AREA NETWORK}

The embodiments below relate to a method of operation of a terminal and an access point that maximizes energy efficiency of a wireless local area network.

IEEE 802.11 is a technology designed to compensate for the shortcomings of Ethernet, which is the current form of wired LAN, and is widely used to minimize unnecessary wiring and maintenance costs at the end of Ethernet networks. An access point (AP) is a device similar to an Ethernet hub. In an infrastructure network model, an access point (AP) enables a group of wireless terminals located around an access point to communicate with each other by connecting them to a network. It allows you to connect to another access point, backbone or WAN network via a connected Ethernet line.

The MAC level of the basic 802.11 standard uses a method called a distributed coordination function (DCF) to share wireless media among multiple terminals. DCF is based on Carrier Sense Multiple Access and Collision Avoidance (CSMA / CA), and optionally uses IEEE 802.11 RTS / CTS to share media between terminals.

The original 802.11 MAC has another coordination function called Point Coordination Function (PCF). This approach is only available in infrastructure mode (infrastructure). Infrastructure mode refers to a manner in which terminals access a network through an access point. This is optional, and in fact few access points or Wi-Fi adapters have this feature.

The access point regularly sends beacon frames (typically one beacon frame every 0.1 seconds). The PCF defines two intervals between these beacon frames. One is a contention free period (CFP) and the other is a contention period (CP). DCF is used in competition. In the non-competition period, the access point transmits a Contention-Free-Poll (CF-Poll) to each terminal in turn. The terminal receiving the CF-Poll has a right to transmit a data frame. In other words, the access point becomes a mediator on competition.

Embodiments of the present invention can provide a technique for reducing the energy consumption of the entire wireless local area network by considering the energy consumption of the remaining terminals when transmitting a single data frame between the terminal and the access point. .

More specifically, embodiments of the present invention consider both energy consumption by one access point and energy consumption by a plurality of terminals, thereby transmitting a single data frame in DCF mode of a wireless local area network. It is possible to provide a technique for accurately calculating the amount of energy consumed.

That is, embodiments of the present invention can provide a technique for maximizing the energy efficiency of the entire wireless local area network by considering the energy efficiency of not only the terminal and the access point that are involved in a single transmission link but also other adjacent terminals.

A method of operating any one of a plurality of terminals communicating with an access point (AP) in a wireless local area network (WLAN) according to an embodiment of the present invention is at least the remaining terminals other than the terminal among the plurality of terminals Determining transmission power and transmission mode based on their energy consumption.

In this case, the energy consumption may be calculated in consideration of the energy consumption by at least one terminal receiving the signal transmitted by the terminal among the remaining terminals.

In addition, the determining may be based on the energy consumption by the access point and the energy consumption by the terminal.

The determining may include calculating a throughput of the wireless local area network based on a communication mode of the wireless local area network; Calculating an energy consumption per unit time of the wireless local area network based on the communication mode; Calculating an energy efficiency of the wireless local area network based on the throughput and the energy per unit time; And determining the transmission power and the transmission mode based on the energy efficiency.

In addition, the performing of the determination may include determining a pair of the transmission power and the transmission mode to maximize the energy efficiency.

In addition, the determining of the pair may be considering a constraint related to the transmission power and a constraint related to the transmission mode.

The communication mode may also include a first mode using a CSMA / CA scheme; And a second mode using the CSMA / CA technique and the RTS / CTS technique.

The calculating of the throughput may include the transmission power, the transmission mode, a probability that data to be transmitted by the terminal exists at a randomly selected slot time, and the access point may successfully receive data transmitted by the terminal. It may be based on at least one of the probability, or the expected value of the payload length.

In the calculating of the energy consumption per unit time, the transmission power, the transmission mode, the probability that there is data to be transmitted by the terminal at a randomly selected slot time, and the access point successfully transmits the data transmitted by the terminal. Probability of receiving a signal, energy consumption of the wireless local area network when successful data transmission, energy consumption of the wireless local area network when collision occurs, or energy consumption of the wireless local area network in an idle period. It may be based on at least one more.

The determining may further include selecting the transmission mode within a plurality of predetermined transmission modes; And setting the transmission power within a range of a predetermined transmission power.

An operation method of an access point communicating with a plurality of terminals in a wireless local area network according to an embodiment of the present invention includes determining a transmission power and a transmission mode based on at least energy consumption of each of the plurality of terminals. do.

In this case, the determining may include calculating a throughput of the wireless local area network based on a communication mode of the wireless local area network; Calculating an energy consumption per unit time of the wireless local area network based on the communication mode; Calculating an energy efficiency of the wireless local area network based on the throughput and the energy per unit time; And determining the transmission power and the transmission mode based on the energy efficiency.

In addition, the performing of the determination may include determining a pair of the transmission power and the transmission mode to maximize the energy efficiency.

The calculating of the throughput may include the transmission power, the transmission mode, a probability that data to be transmitted by the access point exists at a randomly selected slot time, and a destination terminal may determine data transmitted by the access point. It may be further based on at least one of a probability of receiving successfully, or an expected value of payload length.

The calculating of energy consumption per unit time may include the transmission power, the transmission mode, the probability that data to be transmitted by the access point exists at a randomly selected slot time, and the target terminal may determine the data transmitted by the access point. Further based on at least one of the probability of successful reception, the energy consumption of the wireless local area network upon successful data transmission, the energy consumption of the wireless local area network in the event of a collision, or the energy consumption of the wireless local area net in a dormant period. It may be to.

In addition, performing the determination may determine a pair of the transmission power and the transmission mode that satisfies the constraint related to the transmission power and the constraint related to the transmission mode and maximizes the energy efficiency. It may include the step.

1 is a view for explaining a MAC system model according to the IEEE 802.11 standard according to an embodiment of the present invention.
2 is a flowchart illustrating a method of operating a terminal and an access point according to an embodiment of the present invention.
3 is a graph of a simulation result for finding an optimal transmit power according to an embodiment of the present invention.
4 is a graph illustrating a change in energy efficiency of an entire network by varying a transmission distance in a basic mode according to an embodiment of the present invention.
5 is a graph illustrating changes in energy efficiency of an entire network according to different transmission distances in an RTS-CTS mode according to an embodiment of the present invention.

1. System Model

A. PHY level specification of IEEE 802.11n standard

The PHY level of the IEEE 802.11n standard based on Orthogonal Frequency Division Multiplexing (OFDM) scheme provides various transmission rates (see Table 1).

Such transmission rates may be obtained using modulation techniques (eg, BPSK, QPSK, 16-QAM, 64-QAM), convolutional coding technique, and Viterbi decoding technique.

Table 2 summarizes the power consumption characteristics. P _tx , P _ckt , and P _PA are the transmit power, the power consumed by the circuit, and the power consumed by the power amplifier, respectively. Hereinafter, it is assumed that the received power P _rx and the power P _idle in the idle mode are the same as the power P _ckt consumed in the circuit. In addition, the noise power level P _noise is set to -199 dBW.

B. MAC Level Specification of the IEEE 802.11 Standard

The MAC level of the IEEE 802.11 standard supports a contention-based distributed coordination function (DCF) using a polling-based point coordination function (PCF) and a binary exponential backoff (BEB) mechanism.

1 is a view for explaining a MAC system model according to the IEEE 802.11 standard according to an embodiment of the present invention.

Referring to FIG. 1, the wireless local area network 100 according to an embodiment of the present invention includes N terminals 120, 130, and 140 and one access point (AP) 110. At this time, the transmission distance of each of the access point and the N terminals is d _i (i = 1, 2, ..., N). N terminals are located within a communication radius r of the access point. N terminals contend with each other to transmit a data frame in DCF mode.

Each of the N terminals may operate in a basic mode or an RTS-CTS exchange mode. At this time, the maximum transmit power P _{tx , max} of each of the N terminals may be limited to the sum of P _ckt , P _{PA , and max} .

Table 3 shows parameters based on the MAC level of the IEEE 802.11 standard and the legacy mode of the IEEE 802.11n standard.

2. Energy Consumption Analysis of a Wireless Local Area Network According to an Embodiment of the Present Invention

The wireless local area network 100 is based on carrier sensing in DCF mode. Therefore, the terminal that performs actual communication in any time slot and the rest of the terminals other than the access point must decode the received data packet.

For example, assume that the first terminal 120 transmits data to the access point 110. In this case, basically, energy for transmitting data by the first terminal 120 and energy for receiving data by the access point 110 are consumed. As described above, in the DCF mode, the remaining terminals 130 and 140 except for the first terminal 120 receive data transmitted by the first terminal 120 and determine whether the destination of the data is itself. To decode the received data. That is, the remaining terminals 130 and 140 also consume energy to decode the received data.

According to an embodiment of the present invention, the terminal 120 and the access point 110 consider energy consumption consumed by the remaining terminals 130 and 140, thereby consuming energy in the entire wireless local area network 100. It can reduce the consumption.

Hereinafter, it is assumed that N terminals operating in the DCF mode are located in an interference range. However, the scope of the present invention is not limited by these assumptions, and even if a hidden node problem occurs, those skilled in the art may apply the present invention from the following matters. Can be.

In the DCF mode of the wireless local area network, when N terminals operate in a basic mode (BAS) or an RTS-CTS mode (RTS), throughput may be calculated as shown in Equation 1 below.

(Equation 1)

Here, N terminals use i ∈ {BAS, RTS} mode. At this time, Pr _tr = 1-(1-τ) ^N is the probability that there is at least one transmission in a randomly selected slot time, and Pr _s = Nτ (1-τ) ^(N-1) / Pr _tr is the probability of successful transmission. In addition, T _{s , i} is the average time required for successful transmission in the i mode, T _{c , i} is the average time required when a collision occurs in the i mode, T _δ is the idle time.

In addition, when N terminals operate in a basic mode (BAS) or an RTS-CTS mode (RTS) in a DCF mode of a wireless local area network, the energy consumption per unit time may be calculated as shown in Equation 2 below.

(Formula 2)

는 i 모드에서 충돌 발생시 평균 에너지 소모량이다. 이 때,

는 전송 확률, 충돌 확률, 및 충돌된 전송기들의 숫자에 따른 에너지 소모량을 기초로 계산된다. E_δ는 휴지 시간 동안 소모되는 에너지 소모량이다. Where E _{s , i} is the energy consumption during successful transmission in mode i,

Is the average energy consumption when a collision occurs in i mode. At this time,

Is calculated based on transmission probability, collision probability, and energy consumption according to the number of collided transmitters. E _δ is the amount of energy consumed during the down time.

E _{s , i} is energy consumption consumed by one terminal transmitting data, energy consumption consumed by one access point receiving the data, and energy consumption consumed by the remaining (N-1) terminals. It can be calculated as follows.

(Equation 3)

(Equation 4)

Here, T _RTS , T _CTS , T _ACK , T _SIFS , and T _DIFS are described in [Table 3]. T (L, m) is a data size of the IEEE 802.11n standard using a transmission mode m of L bits and may be calculated as shown in Equation 5 below.

(Equation 5)

Here, tPLCPPreamble, tPLCP_SIG, tSymbol are described in [Table 3]. BpS (m) is the number of bits per symbol (bpS) in transmission mode m and is described in [Table 1]. Overhead _bits is the number of bits for overhead including the MAC header, MAC tail, PHY header, and PHY tail.

Meanwhile, T _NAV is a network allocation vector set by RTS frame transmission and has a value of T _SIFS + T _CTS + T _SIFS + T _{(L, m)} + T _SIFS + T _ACK . The remaining terminals and the access point except the terminal transmitting the data receive the RTS packet, and the terminals not involved in the data transmission later set a network allocation vector indicating the end time of the data transmission.

, E_δ는 데이터를 전송하는 하나의 단말에 의해 소모되는 에너지 소모량, 그 데이터를 수신하는 하나의 액세스 포인트에 의해 소모되는 에너지 소모량, 및 나머지 (N-1)개의 단말에 의해 소모되는 에너지 소모량을 포함하며, 다음과 같이 계산될 수 있다.
Also,

, E _δ is the energy consumption consumed by one terminal transmitting data, energy consumption consumed by one access point receiving the data, and energy consumption consumed by the remaining (N-1) terminals. It can be calculated as follows.

(Equation 6)

(Formula 7)

(Equation 8)

In this case, Pr _{c , k} is a probability that k terminals simultaneously transmit data, and may be calculated as follows.

(Formula 9)

Here, _N C _k is a combination of selecting k terminals among N terminals, and τ is a probability that the terminal transmits a data frame at a randomly selected slot time. E _{c , k} is the energy consumption when k terminals simultaneously transmit data, and can be calculated as follows.

(Formula 10)

Accordingly, embodiments of the present invention consider both the energy consumption by one access point and the energy consumption by N terminals, thereby reducing the consumption of a single data frame in the DCF mode of the wireless local area network. The energy consumption can be calculated accurately.

That is, the energy consumption when using i ∈ {BAS, RTS} mode in the wireless local area network of the IEEE 802.11 standard can be calculated as follows.

(Equation 11)

3. Operation method of terminal and access point according to an embodiment of the present invention

2 is a flowchart illustrating a method of operating a terminal and an access point according to an embodiment of the present invention.

2, a method of operating any one of a plurality of terminals communicating with an access point (AP) in a wireless local area network (WLAN) according to an embodiment of the present invention is at least one of the plurality of terminals. And determining the transmission power and the transmission mode based on the energy consumption of the remaining terminals other than the terminal (S200).

In this case, the determining step (S200) may include calculating a throughput of the wireless local area network based on a communication mode of the wireless local area network (S210); Calculating energy consumption per unit time of the wireless local area network based on the communication mode (S220); Calculating an energy efficiency of the wireless local area network based on the throughput and the energy per unit time (S230); And determining the transmission power and the transmission mode based on the energy efficiency (S240).

In addition, in the wireless local area network according to another embodiment of the present invention, a method of operating an access point for communicating with a plurality of terminals includes determining a transmission power and a transmission mode based on at least energy consumption of each of the plurality of terminals. (S200).

In this case, the determining step (S200) may include calculating a throughput of the wireless local area network based on a communication mode of the wireless local area network (S210); Calculating energy consumption per unit time of the wireless local area network based on the communication mode (S220); Calculating an energy efficiency of the wireless local area network based on the throughput and the energy per unit time (S230); And determining the transmission power and the transmission mode based on the energy efficiency (S240).

More specifically, the terminal and the access point according to an embodiment of the present invention can maximize energy efficiency of one access point and N terminals included in the wireless local area network. To this end, the terminal and the access point according to an embodiment of the present invention may select the transmission power P _tx ^* and the transmission mode m ^* as shown in Equation 12 below.

(Formula 12)

는 비연속성(discontinuity)과 비단조성(non-monotonic nature)을 가지므로, 본 발명의 일실시예에 따른 단말 및 액세스 포인트는 완전 검색(exhaustive search) 알고리즘을 이용할 수 있다. 예를 들면, 본 발명의 일실시예에 따르면, 전송 모드의 수는 8개이고, 전송 전력의 범위는 대략 0~1W이므로, 완전 검색 알고리즘을 이용하더라도 계산을 위한 복잡도(complexity)는 높지 않다.

Since has discontinuity and non-monotonic nature, the terminal and the access point according to an embodiment of the present invention may use an exhaustive search algorithm. For example, according to one embodiment of the present invention, since the number of transmission modes is eight and the transmission power range is approximately 0 to 1W, the complexity for calculation is not high even when using a perfect search algorithm.

4. Effects according to embodiments of the present invention

Effects according to embodiments of the present invention can be confirmed by comparing three different techniques using MATLAB simulation.

The first technique is a conventional PHY rate selection technique. At this time, the transmission rate P _tx is fixed to P _{tx, max} . P _{tx and max} are the maximum transmission rates selectable within a predetermined packet error rate (PER). According to an embodiment of the present invention, the PER may be 10 ⁻² .

The second technique is an adaptive transmission power regulation and transmission rate selection technique that maximizes the energy efficiency of a single transmission link. This technique only considers the energy efficiency of one terminal and one access point included in a single transmission link.

The third technique is an adaptive transmission power adjustment and transmission rate selection technique for maximizing energy efficiency of the entire wireless local area network according to embodiments of the present invention. The second and third techniques can also set the PER to 10 ^-2 .

In order to verify the effect according to the embodiments of the present invention, a simulation of varying the transmission distance d may be performed. At this time, it is assumed that the channel is in a slow fading state during the data frame transmission period. That is, it is assumed that channel gain is constant in both the frequency domain and the time domain during the data frame transmission period.

In addition, the bandwidth (bandwidth) is set to 20MHz for the simulation, the number of terminals N is set to 20. At this time, a path loss at the transmission distance d may be calculated as follows.

(Equation 13)

3 is a graph of simulation results for finding an optimal transmit power according to an embodiment of the present invention.

Referring to FIG. 3, the energy efficiency of the terminal changes as the transmission power and the transmission speed are different. At this time, the transmission distance d is fixed at 25 m, and the payload size L is 800 bits (ie, 100 bytes).

According to the second technique 310, when P _tx is 1.64W and the transmission rate is 52Mbps, the energy efficiency of the single transmission link is maximized (311). On the other hand, according to the third technique 320 according to an embodiment of the present invention, when P _tx is 0.99W and the transmission rate is 39Mbps, the energy efficiency 321 of the entire wireless local area network is maximized.

That is, in consideration of energy efficiency of not only a single transmission link but also neighboring terminals according to embodiments of the present invention, energy efficiency of the entire wireless local area network may be maximized.

4 is a graph illustrating a change in energy efficiency of the entire network according to different transmission distances in a basic mode according to an embodiment of the present invention, and FIG. 5 is a transmission diagram in an RTS-CTS mode according to an embodiment of the present invention. This is a graph to explain the change in energy efficiency of the entire network according to the distance.

4 and 5, when the wireless local area network is operated in the basic mode and in the RTS-CTS mode, the energy efficiency of the entire wireless local area network changes as the transmission distance d varies. At this time, according to an embodiment of the present invention, the number N of terminals is 20, and the payload size L is 800 bits (ie, 100 bytes).

The third technique 420, 520 according to an embodiment of the present invention shows the best results over the entire interval (e.g., 0m to 90m) with different transmission distances d. More specifically, the third technique 420, 520 according to an embodiment of the present invention shows an average 34% energy efficiency increase effect compared to the first technique 410, 510.

The methods according to embodiments of the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the equivalents of the claims, as well as the claims.

Claims (16)

In the method of operating any one of a plurality of terminals communicating with the access point (AP) in a wireless local area network (WLAN),
Determining a transmission power and a transmission mode based on at least energy consumption of the other terminals except the terminal among the plurality of terminals;
Method of operation of the terminal comprising a. The method of claim 1,
The energy consumption is
Method of operation of the terminal is calculated in consideration of the energy consumption by at least one terminal receiving the signal transmitted by the terminal among the remaining terminals. The method of claim 1,
The step of determining
And an energy consumption by the access point and an energy consumption by the terminal. The method of claim 1,
The step of determining
Calculating a throughput of the wireless local area network based on a communication mode of the wireless local area network;
Calculating an energy consumption per unit time of the wireless local area network based on the communication mode;
Calculating an energy efficiency of the wireless local area network based on the throughput and the energy per unit time; And
Performing determination of the transmission power and the transmission mode based on the energy efficiency.
Method of operation of the terminal comprising a. 5. The method of claim 4,
Performing the determination is
Determining a pair of the transmission power and the transmission mode to maximize the energy efficiency
Method of operation of the terminal comprising a. The method of claim 5,
Determining the pair
Considering the constraints associated with the transmission power and the constraints associated with the transmission mode. 5. The method of claim 4,
The communication mode is
First mode using CSMA / CA technique; And
Second Mode Using CSMA / CA and RTS / CTS Techniques
Method of operation of the terminal comprising a. 5. The method of claim 4,
The step of calculating the throughput
The transmission power, the transmission mode, the probability that there is data to be transmitted by the terminal at a randomly selected slot time, the probability that the access point successfully receives the data transmitted by the terminal, or the payload length Method based on at least one of the expected value (expected value) of the operation of the terminal. 5. The method of claim 4,
The step of calculating the energy consumption per unit time
The transmission power, the transmission mode, the probability that there is data to be transmitted by the terminal at a randomly selected slot time, the probability that the access point successfully receives the data transmitted by the terminal, the wireless local upon successful data transmission. And further based on at least one of energy consumption of the area network, energy consumption of the wireless local area network when collision occurs, or energy consumption of the wireless local area network in an idle period. Way. The method of claim 1,
The step of determining
Selecting the transmission mode within a predetermined plurality of transmission modes; And
Setting the transmit power within a predetermined range of transmit power
Method of operation of the terminal comprising a.
In the wireless local area network, a method of operating an access point communicating with a plurality of terminals,
Determining a transmission power and a transmission mode based on at least energy consumption of each of the plurality of terminals;
/ RTI > 12. The method of claim 11,
The step of determining
Calculating a throughput of the wireless local area network based on a communication mode of the wireless local area network;
Calculating an energy consumption per unit time of the wireless local area network based on the communication mode;
Calculating an energy efficiency of the wireless local area network based on the throughput and the energy per unit time; And
Performing determination of the transmission power and the transmission mode based on the energy efficiency.
/ RTI > The method of claim 12,
Performing the determination is
Determining a pair of the transmission power and the transmission mode to maximize the energy efficiency
/ RTI > The method of claim 12,
The step of calculating the throughput
The transmission power, the transmission mode, the probability that there will be data to be transmitted by the access point at a randomly selected slot time, the probability that a destination terminal will successfully receive the data transmitted by the access point, or payload And based further on at least one of the expected values of length. The method of claim 12,
The step of calculating the energy consumption per unit time
The transmission power, the transmission mode, the probability that there is data to be transmitted by the access point at a randomly selected slot time, the probability that the target terminal successfully receives the data transmitted by the access point, and the wireless upon successful data transmission. And at least one of energy consumption of a local area network, energy consumption of the wireless local area network in the event of a collision, or energy consumption of the wireless local area network in a dormant period. The method of claim 12,
Performing the determination is
Determining a pair of the transmission power and the transmission mode that satisfies the constraint related to the transmission power and the constraint related to the transmission mode and maximizes the energy efficiency.
/ RTI >

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