KR20170012626A - Sequential Transmission Scheme for Improving Performance of Sub-1GHz WLAN - Google Patents

Abstract

The present invention addresses the problems of the IEEE 802.11ah MAC protocol and suggests a solution thereof. IEEE 802.11ah, a next-generation wireless LAN technology, supports a large number of stations, which can cause network problems when a large number of stations occupy media and transmit data frames.
When a large number of stations are connected, problems such as a hidden node problem occur, a collision occurs between data frames, and an RA frame causes overhead in IEEE 802.11ah.
In the present invention, this problem is solved through a sequential transmission scheme. As a result, it is confirmed that the improvement method has the effect of improving throughput and reducing the media access delay time through simulation using OPNET simulator.

Description

 Sequential Transmission Scheme for Improving Sub-1 GHz Wireless LAN Performance [

Recently, the demand of Internet of Things (IoT), which is a service that connects people, objects, and services to the network and forms an intelligent relationship with each other at any time and place, is increasing. IoT is an evolution from existing USN (Ubiquitous Sensor Network) and M2M (Machine to Machine). If the existing system focuses on communication with devices and people, IoT is not only an end-device of wired / It is characterized by making it possible to communicate objects such as vehicles, telephones, bridges, cultural assets, thermometers, etc., which are commonly seen in the vicinity, to people. In the IoT era, a social network is created that combines objects and people, enabling intelligent collaboration among objects. In addition, things can help people autonomously without human intervention, and people seem to develop to the level of communication and sympathy from providing convenient information between people and devices that can provide various services in connection with desired objects anytime and anywhere.

As interest in IoT service increases, it is necessary to expand the service range of next generation wireless LAN technology. Sub-1GHz next-generation wireless LAN, a technology currently under study for the next-generation wireless LAN, is a wireless LAN technology suitable for IoT service. Currently, IEEE 802.11ah, a sub-1GHz next generation wireless LAN technology, is being standardized. Sub-1GHz Next Generation Wireless LAN is a wireless LAN that uses a frequency band of 1GHz or lower. It is a next-generation wireless LAN that is developed to extend service range to existing wireless LAN and control thousands of terminals with one AP (Access Point). Wireless LAN technology. Because of this feature, sub-1GHz next generation wireless LAN is suitable for IoT environment where many devices should be networked. However, in order to use Sub-1GHz next generation wireless LAN in IoT environment, researches should be conducted considering various problems.

 In the present invention, when a plurality of devices are connected to a network, the performance improvement of the proposed method is confirmed as compared with the conventional method. Simulation was performed for performance analysis.

IEEE 802.11ah, a technology for operating in the sub-1 GHz band, introduced a new concept mechanism called RAW to support a large number of stations.

RAW basically consists of a constant time slot and RAW can be used flexibly according to the size of the network. The AP can assign RAW to one station or station group.

In a small network, RAW can be used as shown in FIG. Assign RAW to each station under the supervision of a beacon. The station transmits the PS-Poll frame for downlink traffic to the AP in the allocated slot, and the AP transmits the data frame.

FIG. 2 shows an uplink and downlink transmission procedure using RAW in a manner different from FIG. First, RAW is divided into RAW1 and RAW2. In RAW1, a PS-Poll frame for connection with the AP is transmitted, and the actual data is transmitted in RAW2. In RAW1, the medium for the PS-Poll frame is allocated to the stations by the AP's authority. If the station is in active mode, the PS-Poll frame indicates that it is ready to be uplinked or downlinked. The AP schedules the stations that requested connection in RAW1, and when RAW2 starts, transmits the RA frame to notify the stations of the scheduling information. The RA frame contains time information for stations to communicate. When each station allocates data traffic uplink or downlink at the allocated time and sends and receives ACK frames, the connection is terminated.

Currently, the most widely used wireless LAN device uses the IEEE 802.11 protocol as a MAC protocol.

Sub-1GHz next-generation wireless LAN, a technology currently under study for the next-generation wireless LAN, is a wireless LAN technology suitable for IoT service. Currently, IEEE 802.11ah, a sub-1GHz next generation wireless LAN technology, is being standardized.

The IEEE 802.11 MAC protocol is mainly based on contention-based Distributed Coordination Function (DCF), and problems arise when the number of stations in the network increases. IEEE 802.11ah is a PCF (Point Coordination Function) based MAC protocol. In order to support a large number of stations, a new concept of RAW is included. RAW can be used flexibly, but problems such as wasted media occur due to the way of using RAW.

In the present invention, problems such as waste of media are improved by using RAW of IEEE 802.11ah, which is a next generation wireless LAN technology.

The improvement method modified the existing MAC protocol. In order to reduce the number of competing stations, stations are divided into station groups. When the station occupies the medium for fairness, the PS-Poll Frame is sent through the competition according to the EDCA of IEEE 802.11e, The DATA frame is the transmission order.

The R-ACK frame is used in the connection process between the AP and the station. An R-ACK frame having the configuration as shown in FIG. 4 has an Order field and indicates a transmission order of a station.

 After polling procedure, station sends DATA frame in order of reservation. Fig. 2 is a basic operation, and has been improved as shown in Fig.

The effect of the invention is increased throughput and reduced media access latency compared to conventional methods. To verify the effect, we experimented using network simulator OPNET.

Using the parameters in Table 1, the number of APs and the number of stations were set to 60 ~ 200.

Figure 6 shows the total throughput of the network. When the number of stations is 60, the channel capacity is already saturated. The improved method shows a certain throughput even though the channel capacity is saturated. On the other hand, the conventional method shows that the throughput decreases when the channel capacity is saturated. As the number of stations increases, collisions increase.

 7 shows the media access delay time of the station. The delay time increases as the number of stations increases as the channel capacity is saturated. The improved method has no additional delay due to the collision, but the existing method shows a larger delay time due to the addition of the delay caused by the collision.

Table 1. Simulation parameters

Fig. RAW-based medium access
Fig. Short frame only RAW
3. Assign RAW to a station group
FIG. R-ACK
Figure 5. RAW transfer procedure
6. Throughput
7. Media Access Delay Time

The present invention improves the performance degradation of IEEE 802.11ah based wireless LAN. To this end, we have made three modifications to the improvement method.

 IEEE 802.11ah uses the Sub-1 GHz band to support wider transmission range and more stations. IEEE 802.11, a conventional wireless LAN standard, causes various problems when supporting a large number of stations. To avoid a large number of stations competing at one time, the stations are divided into station groups and RAWs are assigned to station groups as shown in FIG.

 The allocated RAW is divided into CTW (Control Traffic Window) for polling the station and DTW (Data Transmission Window) for transmitting the DATA. In the CTW, the station sends a PS-Poll frame to inform the AP that it is ready for DATA transmission. The AP transmits an R-ACK frame including an Order field as a response in FIG. R-ACK modified the Duration field of the ACK frame to the Order field. The Order field is incremented by 1 to inform the station of the transmission order, and the station performs data transmission in the DTW according to the transmission order.

 In the DTW, a station performs a DATA transmission without transmitting an RA (Resource Allocation) frame that causes overhead in the conventional method. The RA frame is a frame for informing the station of the scheduling information. In the CTW procedure, since the station knows its transmission order, it does not need to receive information from the RA frame. By not sending the RA frame in this way, the network overhead is reduced.

Claims (2)

R-ACK frame notation as response frame to PS-Poll frame Transfer procedure of RAW

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