KR100924753B1 - Channel Allocation Method using Power Controlled CTS in Multi-hop Networks - Google Patents

Abstract

The present invention relates to a method for allocating a CTS power control channel for a multi-hop network, and more particularly, to a wireless communication method comprising exchange of a request-to-send (RTS) signal and a clear-to-send (CTS) signal. The RTS transmit power of the transmitting node is fixed, and the CTS transmit power of the receiving node is determined to be received only by nodes located within an interference region set to satisfy the target SINR of the receiving node. CTS power control channel allocation method. According to the present invention, it is possible to provide a method for allocating a CTS power control channel for a multi-hop network by fixing a data transmission power and adjusting a CTS frame transmission power to reduce a communication area occupied by a transmitter and a receiver, thereby increasing communication space reuse. have.

RTS, CTS, Interference Zone, CTS Power Control, Data Transmission Power

Description

Channel Allocation Method using Power Controlled CTS in Multi-hop Networks

The present invention relates to a method for allocating a CTS power control channel for a multi-hop network that increases the communication space reuse rate by adjusting the CTS frame transmit power to reduce the communication area occupied by the transmitter and the receiver.

As wireless communication network technology advances, the importance of spatial reuse to increase overall system throughput has increased. The media access control (MAC) scheme in the IEEE 802.11 standard has also been studied to achieve higher throughput through reuse of communication space.

Due to the rapid development of the wireless network technology, the service requirements of each user are diversified, and as a result, the importance of the radio resource management method for improving the system throughput is highlighted. As a network access protocol, the IEEE 802.11 standard is widely used for wireless data communication. In particular, in the 802.11n standard for high-speed data rate communication, multiple antenna (MIMO) and OFDMA technologies are proposed as main technologies of the physical layer (PHY layer). However, the efficient MAC layer design is also very important because throughput performance in SAP (service access point) depends not only on the physical layer but also on the MAC layer. In multi-hop wireless network environment, reuse of communication space is just as important because interference of other neighboring communication users has a major influence on channel environment.

Therefore, studies on various MAC schemes and interference areas for communication space reuse have been proposed to be incorporated into the IEEE 802.11 standard. However, the existing research mainly used the method of adjusting the data transmission power.

In Ref. [5], the author defined the transmission domain, carrier sensing domain, and interference domain, and analyzed the efficiency of the RTS-CTS exchange scheme. However, the hidden terminal problem still occurs in the region that does not receive the RTS-CTS transmission. If the distance between the transmitter and the receiver is greater than or equal to the boundary value, the interference region of the receiver is larger than the CTS transmission region. To solve this problem, a conservative CTS scheme has been proposed. In this scheme, the CTS is transmitted only when the RTS received signal is greater than or equal to the threshold. This approach can increase the reliability of the wireless link even though it reduces network connectivity.

In the following references [1]-[4] the power control scheme was studied. In references [1], [3], and [4], studies have been proposed to alleviate hidden terminal problems and to improve spatial reuse. Power controlled multiple access (PCMA) in Ref. [1] uses a busy tone to inform channel usage of neighboring nodes and uses Request-Power-to-Send (RPTS) and Acceptable-Power-To to determine data transmission power. Send and receive (APTS) messages.

The present invention proposes an improved MAC technology using a power control CTS. Unlike the existing research, the method according to the present invention adjusts the CTS transmission power based on the receiver, while fixing the data transmission power. This is because when the data transmission power is adjusted, the interference area is changed according to the transmission power, which makes it difficult to detect the interference area and control the network. Low transmit power creates a larger interference area than without power control. Therefore, the method according to the present invention does not change the data transmission power to facilitate the control of the interference region at the receiving end.

Reference

[1] JP Monks, V. Bharghavan, and WW Hwu, "Power Contolled Multiple Access Protocol for Wireless Packet Networks", in Proc . IEEE INFOCOM , 2001.

[2] D. Qiao, S. Choi, A. Jain, and KG Shin, "MiSer: An Optimal Low-Energy Transmission Strategy for IEEE 802.11a / h", in Proc . ACM MobiCom , 2003.

[3] Y. Zhou and SM Nettles, "Balancing the Hidden and Exposed Node Problems With Power Control In CSMA / CA-Based Wireless Networks", in Proc . IEEE WCNC , 2005.

[4] T.-S. Kim, H. Lim, and JC How, "Improving Spatial Reuse through Tuning Transmit Power, Carrier Sense Threshold, and Data Rate in Multihop Wireless Networks", in Proc . ACM MobiCom , 2006.

[5] K. Xu, M. Gerla, and S. Bae, "How Effective is the IEEE 802.11 RTS / CTS Handshake in Ad Hoc Networks?", In Proc . IEEE GLOBECOM , 2002.

An object of the present invention for solving the above-described problems, CTS power for a multi-hop network to increase the communication space reuse rate by fixing the data transmission power, adjusting the CTS frame transmission power to reduce the communication area occupied by the transmitter and the receiver It is to provide a control channel allocation method.

CTS power control channel allocation method for a multi-hop network according to the present invention for achieving the above object, a wireless communication scheme consisting of exchange of request-to-send (RTS) signal and clear-to-send (CTS) signal RTS transmit power of the transmitting node is fixed, and the CTS transmit power of the receiving node is determined such that the CTS signal can be received only by nodes located within an interference region set to satisfy the target SINR of the receiving node. It is characterized by.

에 의해 정해지는 것을 특징으로 한다.In addition, in the CTS power control channel allocation method for a multi-hop network according to the present invention, P ₀ is the RTS transmit power at the transmitting node and P _R is the RTS receiving power at the receiving node. When the noise power at the receiving node is N ₀ and the SINR threshold at the receiving node is S ₀ , the CTS transmit power p of the receiving node is

It is characterized by.

In addition, in the method of allocating a CTS power control channel for a multi-hop network according to the present invention, in the IEEE 802.11e network communication scheme having a TXOP frame structure, the transmitting node allocates TXOP by exchanging RTS and CTS signals with the receiving node. Receiving first step; And a second step in which a third node that has received the RTS signal of the transmitting node but has not received the CTS signal from the receiving node reserves time for BlockAckReq and BlockAck by avoiding TXOP periods of the transmitting node and the receiving node; And a third step of performing communication by exchanging RTS and CTS signals with the fourth node.

According to the present invention, it is possible to provide a method for allocating a CTS power control channel for a multi-hop network by fixing a data transmission power and adjusting a CTS frame transmission power to reduce a communication area occupied by a transmitter and a receiver, thereby increasing communication space reuse. have.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In Chapter 1, we introduce the power control CTS and interference domain, and in Chapter 2, we propose a method to apply the proposed scheme to IEEE 802.11e system. In Chapter 3, the analysis shows the throughput performance of the proposed method.

1. CTS transmission power control considering interference area

For channel allocation, the interference area of the receiver that directly affects the spatial reuse of the receiver is used. The interference area is an area around the receiver, and when another transmission occurs in the area, an interference occurs and the SINR of the receiver is less than a certain threshold value. The interference region is changed by the distance between the transmitting end and the receiving end, the SINR boundary value, and the transmission power.

SINR stands for signal-to-interference plus noise-ratio, which is the power of thermal noise (AWGN) in the background with respect to the signal power, and that of other transmission pairs that are simultaneously being transmitted in the vicinity. The ratio of the sum of the signal power, that is, the interference signal power, which is an unwanted signal.

If another transmitter around the receiver starts transmitting, the target receiver will have a lower SINR. Assuming a simple channel model in which the channel environment is determined by path loss, the radius of the interference region may be expressed by Equation 1 below.

는 SINR threshold이다. 또한, α는 거리 감쇄의 지수를 의미한다.Here, R is the distance of the transmitting and receiving end,

Is the SINR threshold. In addition, α means the index of distance attenuation.

1 is a diagram illustrating an example of a transmission area and an interference area.

가 2R이라고 가정한다. 만약 2개 이상의 전송 노드가 서로 간섭을 준다면 전송 충돌이 발생한다.1 shows an example of a transmission area of node STA 1 and an interference area of STA 2. In this example

Assume is 2R. If two or more transmitting nodes interfere with each other, a transmission collision occurs.

To avoid this collision, each transmitter must verify that other active receivers are in the transmission range. Each receiver must also verify that there is an active transmitter in the interference region before transmission.

The concept of the interference region may also be applied to the virtual carrier sensing model in the IEEE 802.11 MAC using RTS-CTS. If the node is in the transmitting area of the transmitter, it stops the transmission when it receives the RTS transmitted to another node. This is because the newly started transmission affects the CTS or ACK reception of the previous transmission. In the same principle, a node existing in the interference region of the target receiver cannot start transmission when it hears a CTS destined for another node. This may cause the reception of data at the target receiver to fail.

1.1 Power Control CTS Principle

In the CTS power control channel allocation method for a multi-hop network according to an embodiment of the present invention, the transmission power of the CTS frame is determined based on the reception power of the RTS frame.

Transmission of the CTS frame needs to be received by nodes located within the interference region around the target receiver. This is because the interference node interferes with the transmission from the receiving node's point of view, so that the CTS frame is transmitted to prevent simultaneous transmission of such interference nodes.

To explain the basic principle of CTS transmit power control, we consider the transmitting node, receiving node and interfering interfering node.

When the transmitting node transmits the RTS with the fixed power P ₀ , the received power becomes P _R = P ₀ g _TR in consideration of the distance reduction g _TR between the transmitting and receiving ends.

The receiving node responds with a power-controlled CTS at p, where the interfering nodes on the boundary of the region capable of overhearing the CTS satisfy the following condition (2).

Where g _RI is the channel gain between the receiving node and the interfering node, N ₀ is the noise power at the receiving node, and S ₀ is the SINR threshold at the receiving node. Since the noise power at the interfering node is also about the same as the noise power at the receiving node, N ₀ is also the noise power at the interfering node.

That is, Equation 2 successfully receives the received SINR of the interfering node and receives the CTS signal because the interfering node on the boundary line of the interfering region should successfully receive the power controlled CTS signal of the receiving node to prevent simultaneous transmission. It is set to S _{0 which} is a possible threshold. When the SINR of the interfering node at the boundary of the interfering region becomes S ₀ , the SINR of the interfering node in the interfering region becomes larger than S _0. Therefore, if the requirements of Equation 2 are satisfied, the power-controlled CTS signal of the receiving node becomes the interfering region. It is successfully received by the nodes within it.

If the interfering node starts another RTS transmission while the transmitting node is transmitting data, the SINR at the receiving node is expressed by Equation 3 below.

Where N ₀ is P ₀ g _RI Equation 3 holds because it is significantly smaller. Of course, the interfering node transmits the RTS signal at a fixed power P ₀ .

Equation 3 is a condition that the target SINR of the receiving node must satisfy the threshold S ₀ even if any other interference signal exists. That is, since nodes within the interference region have received the CTS signal, the RTS transmission cannot be performed, and the interference nodes outside the interference region can transmit the RTS. P ₀ g _RI , which is the reception power of the RTS signal from the interference node of the receiving node Is the largest when the interference node on the interference boundary line transmits the RTS signal, and Equation 3 is established.

Through Equations 2 and 3, the CTS transmit power in the CTS power control channel allocation method for a multi-hop network according to an embodiment of the present invention is determined as in Equation 4 below.

In this power control CTS scheme, the receiver determines the transmit power of the CTS in inverse proportion to the received RTS power.

Nodes in the interference zone around the receiving node receive the CTS frame, so that nodes in the interference zone cannot be transmitted simultaneously, whereas nodes outside the interference zone of the current receiving node can transmit simultaneously, thus allowing for spatial reuse. Increases efficiency

2. Application of IEEE 802.11e Network to the Power Control CTS Scheme

In a wireless LAN (WLAN) network environment, the number of Access Points (APs) using the same channel in a given space is increasing. If there are not many access points in space, the interference problem can be solved by allocating different channels between neighboring access points. However, with the emergence of many service providers and the emergence of mesh networks as urban wireless network infrastructures, there is an increasing possibility that there will be neighboring access points using the same channel.

The IEEE 802.11 standard essentially defines the physical and MAC layers between one hop distance and does not address the interference between access points. In this case, the RTS-CTS method can be used as a way to solve the hidden terminal problem, but it is inefficient in terms of spatial reuse. As a result, installing multiple access points within a given area will not contribute to an improvement in overall system throughput.

2 and 3 are structural diagrams of an RTS-CTS range and its TXOP in an existing IEEE 802.11e system, respectively.

2 and 3, in the existing IEEE 802.11e system, transmission is made with a transmission opportunity (TXOP frame structure). TXOP is defined as a time interval in which a communication terminal (STA) is guaranteed transmission rights. Such TXOP may be obtained through a competition base itself, and may also be allocated through a hybrid coordinator (HC) which is a function of an access point. The contention-based IEEE 802.11e uses an enhanced distributed channel access (EDCA) scheme, wherein the contention-based TXOP is called EDCA TXOP. In addition, TXOP allocated by HC is called Polled TXOP. Each TXOP transmits a plurality of frames and then checks the transmission result with BlockAck (block acknowledgment) at a time.

The CTS power control channel allocation method for a multi-hop network according to the present invention is intended to be modified and applied.

First, use the CTS to adjust the transmission power. Secondly, a node that overhears a CTS cannot start transmission, but if a node overhears an RTS, it can start a new transmission. This modification can solve the exposed terminal problem. Third, an ACK transmission failure that may occur by ignoring the RTS transmitted to another node may be resolved through a reservation for ACK reception.

4 and 5 are RTS-CTS ranges and TXOP structure diagrams according to the CTS power control channel allocation method of the present invention, respectively. That is, FIGS. 4 and 5 show a modified technique by applying the proposed CTS power control.

4 and 5, as in the conventional TXOP scheme, STA 1 is allocated a TXOP by exchanging RTS-CTS with STA 2. In this case, STA 2 transmits a power controlled CTS, and STA 3 receives interference from STA2 but cannot receive CTS. Since the STA 3 receives the RTS from the STA 1, the STA 3 can know the TXOP period and thus can reserve time for BlockAckReq and BlockAck.

In the method of the present invention, the STA3 may transmit its own RTS by recycling the communication space, and the STA4 may respond to the STA3 through the CTS.

Therefore, the method according to the present invention can generate more transmission / reception stages in a given area than the conventional scheme.

The present invention can be applied to both EDCA TXOP and Polled TXOP because only the TXOP internal structure has been changed. In the case of EDCA TXOP, there is a competition section through backoff before the RTS transmission, and the TXOP section is determined as the TXOP limit value of the RTS frame. In the case of polled TXOP, the TXOP allocation is determined by the AP through a polling message.

3. Performance Analysis

In this chapter, the communication occupied area is first calculated to compare the spatial reuse performance of the existing RTS-CTS scheme and the CTS power control channel allocation method according to an embodiment of the present invention.

For the performance analysis of the interference area control method through the CTS power control of the present invention, it is assumed that the distance between the transmission and reception nodes is shorter than half of the transmission area and the interference area is twice the distance between the transmission and reception nodes.

If the distance between the transmitting and receiving nodes is set to x, the communication occupied area A (x) of the conventional RTS-CTS scheme is expressed by Equation 5 below.

Where R is the radius of the transmission region.

On the other hand, the communication occupied area B (x) of the CTS power control channel allocation method of the present invention is shown in Equation 6 below.

According to the distance x, the occupied area can be derived as shown in Equation 7 below.

를 계산하였다. 그 결과, 기존의 데이터 전력제어 방식(Simple 전력제어 CTS)의 경우 기존 방식보다 9.62% 좁은 점유영역을 차지한다. 이러한 Simple 전력제어 CTS는 RTS 수신 주변 노드들이 동시 전송을 할 수 없기 때문에 통신공간 재활용(spatial reuse) 측면에서 한계가 있다.Similarly, the average occupied area of the conventional data power control method

Was calculated. As a result, the existing data power control method (Simple Power Control CTS) occupies 9.62% narrower than the conventional method. Such a simple power control CTS has a limitation in terms of spatial reuse since the neighboring nodes of the RTS receiver cannot transmit simultaneously.

In order to further increase communication space recycling efficiency, a method of allowing simultaneous transmission of RTS receiving nodes is a CTS power control channel allocation method according to the present invention. Let's define the area where RTS-only range exists where only nodes receive RTS and not receive CTS.

In FIG. 6, the power controlled CTS region according to the present invention is an occupied region by a transmission pair of STA 1 and STA 2. Since STA 3 does not belong to the CTS region of STA 2, it may transmit a new RTS to STA 4.

The transmission area and the reception area may show the probability that a link between STA 3 and STA 4 is generated. If the communication terminals STA are uniformly distributed, the probability of generating a new transmission pair may be represented by the ratio of the transmission area to the reception area. This probability varies depending on the positions of STA 3 and STA 4 and the distance between STA 1 and STA 2.

Let the position of the transmitting node STA3 within the RTS-only area be y ₁ and the position of this receiver STA4 be y ₂ . In addition, when the transmission link generation indicator function is defined as I (x; y ₁ ; y ₂ ), it means 1 when transmission occurs and 0 in other cases.

here The probability of generating a transmission pair according to y ₁ is given by Equation 8 below.

The communication occupied area C ( x ) of the present invention is represented by the following equation (9).

Where R ( x ) is the area of the CTS region.

By calculating this, the average occupation area can be obtained by the following equation (10).

Through performance analysis, we can see that the proposed method occupies 46.7% less area than the existing RTS-CTS method. The DATA power control scheme [3], which includes the interference region of the receiver, occupies 81.8% of the existing scheme region.

Table 1 compares the occupied areas normalized to the occupied areas of the existing IEEE 802.11 system. The method according to the invention shows the narrowest occupied area and consequently shows high spatial reuse performance.

Let's look at the performance improvement of the proposed method. SINR at the receiving end STA 2 is expressed by Equation 11 below.

SINR at the receiver STA 4 is also represented by Equation 12 below.

Here g _ij (x) means a distance attenuation coefficient between STA (i) and STA (j).

Using the SINR above, the data rate is calculated by the following equation (13) using Shannon's capacity formula.

The network throughput performance according to the transmit / receive end distance x is given by Equation 14.

A _{R -O} means the area of the RTS-only area. Finally, average throughput performance is derived as in Equation 15 below.

7 and 8 compare the system throughput performance according to the noise power N ₀ . It is assumed that the transmission distance R is 100m and the transmission power P ₀ is 1W. In performance analysis, the absolute values of transmission power and noise do not have a significant effect on performance. In the data power control scheme, the transmit power is adjusted to include the interference region of the receiver. To calculate the system capacity, C ₁ and C ₂ were set to 1 and the distance attenuation index was set to -4. The method according to the present invention (indicated as "Proposed" in Figs. 7 and 8) showed the highest system throughput performance, and the performance difference with the conventional scheme increases as the noise power increases. The noise power ^1.0 (marked as "DATA power control" in Figs. 7 and 8) ⁹ W days when the data power control scheme of 12.8% compared to, and the noise power ^1.0 in ⁸ W shows the improvement of the 28.4% throughput performance . Through the performance derivation, the proposed method shows the highest throughput performance and it can be confirmed that this is the effect of high spatial reuse.

4. Conclusion

As described above, in one embodiment of the present invention, a power control CTS scheme is proposed as a method for improving system throughput performance. In the method of the present invention, the RTS and data transmission are fixed power while the CTS frame only performs power control in consideration of potential interference. Since data is transmitted with a fixed power, the interference area becomes constant when the position of the receiver is fixed. The conventional RTS-CTS method and the data power control method are compared with the method of the present invention in terms of average transmission occupancy area and system throughput. As a result, the proposed scheme showed significant throughput improvement due to the high reuse of communication space. In addition, the proposed scheme has a low implementation complexity by reducing the overhead of exchanging information on interference areas of other transmission nodes required for data power control.

The present invention is not limited to the above-described preferred embodiments and can be easily modified by anyone of ordinary skill in the art without departing from the gist of the invention claimed in the claims, Such changes are intended to fall within the scope of the claims.

1 illustrates an example of a transmission area and an interference area;

2 and 3 are structural diagrams of an RTS-CTS range and its TXOP in the conventional IEEE 802.11e system, respectively.

4 and 5 are RTS-CTS range and its TXOP structure diagram according to the CTS power control channel allocation method of the present invention, respectively.

6 is a view showing that the power controlled CTS region according to the present invention is an occupied region by a transmission pair of STA 1 and STA 2.

7 and 8 are diagrams comparing system throughput performance according to noise power N ₀ .

Claims (3)

delete In a wireless communication system consisting of exchange of request-to-send (RTS) signals and clear-to-send (CTS) signals, The RTS transmit power of the transmitting node is fixed, and the CTS transmit power of the receiving node is determined such that the CTS signal can be received only by nodes located within an interference region set to satisfy the target SINR of the receiving node, When the RTS transmit power at the transmitting node is P ₀ , the RTS receiving power at the receiving node is P _R , the noise power at the receiving node is N ₀ , and the SINR threshold at the receiving node is S ₀ , CTS transmit power p of the receiving node,

C.S power control channel allocation method for a multi-hop network, characterized in that determined by. The method of claim 2, In the IEEE 802.11e network communication scheme having a TXOP frame structure, The first step in which the transmitting node is allocated TXOP by exchanging RTS and CTS signals with the receiving node; And A second step of receiving a RTS signal of the transmitting node but not receiving the CTS signal from the receiving node to reserve time for BlockAckReq and BlockAck by avoiding TXOP periods of the transmitting node and the receiving node; And And a third step of performing communication by exchanging RTS and CTS signals with a fourth node. 3.

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