KR101057914B1 - Dynamic Topology Control Method for Multi-hop Relay in Cellular TD-OPDM System - Google Patents

Abstract

The present invention relates to a dynamic topology control method for a multi-hop relay in a cellular time division orthogonal frequency division multiple access (TDD-OFDMA) system, wherein the dynamic topology control method of the present invention is K (K≥2). A resource reuse step of sub zones of the divided relay zone being reused in another layer; A relay layering step of placing the relays (RSs) in layers of another layer; And a relay grouping step of finding a set of repeaters RSs connected to the same upper repeaters RS of the upper layer.

According to the present invention, it is possible to improve the quality and performance of a multi-hop relay link by adjusting interference generated when resources are reused for a relay link in a multi-hop relay system according to traffic load of each relay link.

Description

DYNAMIC TOPOLOGY CONTROL METHOD FOR MULTI-HOP RELAYING IN A CELLULAR TDD-OFDMA SYSTEM}

The present invention relates to a wireless communication method, and more particularly, to a dynamic topology control method for a multi-hop relay in a cellular time division orthogonal frequency division multiplexing (TDD-OFDMA) system.

IEEE 802.16j's TDD-OFDMA based multi-hop relay system is a useful means for extending the coverage, yield and capacity of mobile wireless broadband such as mobile wireless metropolitan area network (MAN). The multi-hop relay system includes a relay station (RS) that supports a wireless relay function in the middle for a mobile station (MS) connection, and a base station that supports a wireless relay function by directly connecting with an MS or RS through a wireless link. (MR-BS).

1 is an exemplary diagram showing a frame structure of a non-transparent mode when N = 2. Where N is the number of hops for the termination connection. As shown in FIG. 1, one TDD frame is divided into an uplink and a downlink, and each link includes an access zone for allowing the MS to directly communicate with the MR-BS or RS, and between the MR-BS and RS. It is divided into a relay zone for providing a link. The main feature of this particular frame structure is that the access zone can be shared with all MSs communicating directly with the MR-BS or indirectly via RSs. Thus, the access zone must be scheduled independently of the MR-BS and RSs to allow dynamic bandwidth reservation between MSs. In non-transparent mode, where MSs cannot receive control messages directly from BS, bandwidth allocation result notification via MAP message must be relayed with data delivery. On the other hand, the relay link is divided orthogonally for multiple RSs. Therefore, each RS must have a specific bandwidth allocation notification (eg, downlink MAP message).

The data rate of each zone depends on the channel status of the individual links. The signal-to-interference noise ratio (SINR) of the link may be a channel quality indicator for determining the appropriate mode of adaptive modulation and coding (AMC).

When the coverage of a large area is secured by a plurality of RSs, there may be a case of three hops or more between the MS and the BS. In this case, the relay zone may be time-divided into multiple subzones. As shown in Figure 2, each subzone is reserved for the next relay link. At this time, a virtual plane defined by RSs having the same hop to reach the BS is defined as a layer. For example, in FIG. 2, the RSs in Layer 2 require two hops to connect with the BS, while the RSs in Layer 1 connect directly to the BS in one hop. The subzone allocated to the RSs of the upper layer needs larger capacity because it must process the merged traffic for transmission to the RSs of the lower layer. Thus, as shown in FIG. 2, the subzones must be appropriately divided to regulate relay traffic throughout the cell.

In the frame structure of FIG. 2, the available resources for each subzone are critically limited in accordance with the number of hops required for increasing the number of end connections. If N is too large, the Nth subzone will be almost null. To handle this particular situation, subzones can be reused by RSs of other layers, to the extent that co-channel interference can be tolerated. For example, in FIG. 2, RS5 and RS6 of layer 3 may share subzone 1 with MR-BS. Similarly, subzone 2 can be reused in layers 2 and 5. In general, a relay zone may be divided into K subzones, and the divided subzones may be reused in another layer. This special reuse strategy is called reuse-by-K. As shown in FIG. 3, each subzone has one of three states (listen, send and idle).

3 shows a reuse 1/3 scheme, in which the dashed line represents co-channel interference. Since the same subzones are shared by RSs three hops away from each other, the co-channel interference indicated by the dotted lines in FIG. 3 does not seem severe to the same kind of RSs. However, in a real network, the difference in the number of hops existing between RSs may not be proportional to the difference in physical distances. 4 shows an example of configuring a network by applying a 1 / K frame structure of K = 3. While generalizing the relay resource reuse scheme to 1 / K, it was expected that sufficient distances would be secured between RSs having a 2-hop difference. However, as shown in FIG. There is a situation that the link quality of RS2 is degraded because the distance cannot be secured. In general, the position of RS is installed in a large number of unspecified areas as needed rather than arranged at regular intervals, so if the link configuration is wrong, even if the reuse method using the 1 / K frame structure is applied, such other hop-to-hop interference problem may occur. May occur.

Meanwhile, since RSs belonging to the same layer reuse the same resources, another kind of co-channel interference called inter-branch interference (indicated by a dashed-dotted line in FIG. 3) may depend on their reuse distance. This can be another serious problem for reuse 1 / K. For example, as shown in FIG. 3, the RS1 signal may be co-channel interference to RS4 while RS2 transmits to RS3 and vice versa.

This aspect of interference can be controlled through topology control that controls the connectivity of the links. Control of the interference pattern will control the quality of each link. Controlling the interference added to a specific link changes the aspect of interference of other relay links, so the quality of each link is trade-off. To improve the overall network performance, the quality of each relay link in this relationship can be controlled in the direction of maximizing end-to-end capacity. The delay is not reduced. Therefore, a method of securing link quality in proportion to the amount of traffic weighted on each link is more suitable. For example, in FIG. 5 (a), the link of RS2 due to inter-hop interference and RS7 due to inter-branch interference have a lower capacity than the traffic amount. When the topology is transformed into the form as shown in Fig. 5 (b), the capacity of RS4 is reduced from 8 to 5, but it is sufficient to accommodate the traffic weighted to RS4, and instead of the loss of capacity of the RS4 link, RS2 and RS7 are more than before. Higher capacity means more traffic for the entire network.

Therefore, there is an urgent need for a topology control method for interference distribution that secures a large link capacity on a link to which a large amount of traffic is weighted while controlling the above interferences.

Another object of the present invention is to provide a dynamic topology control method capable of controlling inter-hop interference and relay branch interference according to resource reuse in a multi-hop relay network in consideration of traffic load between relay links.

In accordance with another aspect of the present invention, there is provided a dynamic topology control method including: a resource reuse step in which subzones of K (K≥2) divided relay zones are reused in different layers; A relay layering step of placing the relays (RSs) in layers of another layer; And a relay grouping step of finding a set of repeaters RSs connected to the same upper repeaters RS of the upper layer.

The relay layering method of the present invention for achieving the above object, (a) measuring the signal-to-interference and noise ratio (SINR) of the link between the repeater and the base station to select the repeaters having the best connection with the base station to the set of repeaters belonging to Layer 1 Forming a; (b) further selecting repeaters that may be included in layer 1; (c) selecting a repeater having the best connection with the layer 1 to form a set of repeaters belonging to layer 2; (d) forming a set of repeaters which may have lower repeaters in the layer 2; And (e) additionally selecting repeaters that may be included in layer 2.

In order to achieve the above object, the relay grouping method of the present invention includes the steps of: (a) selecting a repeater having a minimum signal-to-interference noise ratio (SINR) in a link with a higher repeater in a higher layer in a higher layer of the target group; ; (b) determining a temporary upper repeater and a temporary effective delay for each repeater belonging to a set of lower repeaters of the test repeater; And (c) selecting an upper repeater according to the temporary effective delay.

According to the dynamic topology control method of the present invention through the above configuration, the quality and yield of the multi-hop relay link by adjusting the interference caused by reusing resources for the relay link in the multi-hop relay system in consideration of the traffic load for each relay link It can improve performance.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and that additional explanations of the claimed invention are provided. Reference numerals are shown in detail in preferred embodiments of the invention, examples of which are indicated in the reference figures. For all possible cases, like reference numerals are used in the description and the drawings to refer to the same or like parts. Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention.

The present invention is largely composed of two stages: RS rayering and RS clustering. RS layering is a procedure for placing RSs in the appropriate layers of another layer. RSs that can reach the BS with the same number of hops are treated as being on the same layer. The purpose of RS layering is to minimize inter-hop interference. Since resources used for relay link in one layer are reused for relay link in other layers, RS layering is for placing RSs in different layers to minimize co-channel interference with each other.

On the other hand, RS aggregation is a procedure for finding a set of RSs of a lower layer connected to the same upper RS of an upper layer. For given RS layers, RS aggregation is to determine the sets of RSs that are connected to the same RS of the upper layer in the lower layer.

The two steps described above are in turn a hierarchical RS aggregation procedure, as shown in FIG. In Figure 6 Layer 1 does not need RS aggregation because in BS 1 the BS is connected to all RSs. That is, in the layer 1, all RSs belong to one cluster.

In the following descriptions and definitions of letters and terms used to describe RS layering and RS aggregation according to the present invention are as follows.

S : set of all RSs. R _k ∈ S

H _n : set of RSs belonging to layer n

H _{n , S} : A set of RSs that can have lower RSs in the next layer. H _{n , S} ⊂ H _n

Each RS in the tree structure must have its own unique upper RS.

s _k : high RS of r _k

Q _k : set of lower RSs of r _k

l _{k, l:} r _k from the RS to the RS link, ranging r _l

C _{k, l} : l _{k, l} data rate (bits / sec)

τ _k : Traffic load of r _k (bits / sec)

The traffic load on each link can be normalized by the corresponding link capacity.

The traffic load index is defined as follows.

LF _k = τ _k / C _{m , k} where m is r _m = s _k Same as

RSS _{l, m} : signal strength of r _l received from r _m

An interference index indicating the relative strength of the r _k signal with respect to the higher RS signal received by another RS is defined as follows.

_Given the traffic load and load index for Q _k , the capacity between hops is defined as

The traffic concentration index is defined as follows.

여기서

here

The average of the traffic concentrations for all RSs in each layer is as follows.

The traffic concentration index is used to determine whether to accept load balancing and interference control.

An effective delay of layer n is defined as an equivalent unit for transmitting 1 bit to all RSs of a layer from BS to n as follows.

Τ _{ete, n} is the sum of the traffic loads with the end points of all RSs belonging to layers up to n .

7 is a flowchart illustrating an RS layering method according to the present invention. Referring to FIG. 7, first, signal-to-interference noise ratio (SINR) of the direct link between each RS and BS is measured to select RSs having the best MCS mode, that is, RSs having the best connection with the BS. The selected RSs form a set H _{1 of} RSs belonging to layer 1 (S701). If this is expressed as an expression, it is as follows.

Where C _{0 , k} is the data rate on the link between BS and RS r _k . Since the data rate is defined by the MCS mode dependent on the SINR of the link, there can be multiple RSs in the set H ₁ . That is | H ₁ | ≥1.

In the next step, the remaining RSs, except for the RSs included in H ₁ , are indexed again according to the received signal strength (RSS) order to form the candidate set U of the layer 1 as follows (S703).

U = S - H ₁

Next, additional RSs capable of achieving greater capacity by direct connection to the BS than through the RS already selected as an element of H ₁ are searched for and selected (S705). In the case of r _k ∈ U , the corresponding RSs can be found by evaluating the following delay criteria in descending order of RSS as measured at BS.

On the right side of the inequality in Equation 3, the second term | H ₁ | Each time a new RS is included in H ₁ , it is removed from U. In other words,

Thereafter, steps S703 and S705 are repeated until no more RSs can be included in H ₁ (S707). Through this process, Layer 1 is determined.

Given H ₁ , RS having the best MCS mode is selected as H ₂ by the following equation (S709).

Then, a set of RSs which may have a lower RS is given by the following equation (S711).

Where η _th is a threshold for removing RSs that cause excessive interference. This step reduces the number of RSs that can potentially interfere with the RSs of the upper layer if they have a lower RS.

After this process, the candidate set of the layer 2 is given as follows (S713).

For r _k ∈ U , additional RSs capable of achieving greater capacity through H _{1, S} than through H _{2, S} RS are subject to the following delay criteria in the RSS descending order of the BS measured at each RS. Is selected as H ₂ (S715).

그런 다음, H ₂ 에 포함될 수 있는 RS가 더 이상 발견되지 않을 때까지 단계 S711 내지 S715가 반복된다(S717). 이와 같은 과정을 거쳐 레이어 2가 결정된다.Each time a new RS is included in H ₂ , it is removed from U. In other words

Then, steps S711 to S715 are repeated until no more RS can be included in H ₂ is found (S717). Through this process, layer 2 is determined.

in the case where n≥3 for H _n H and _{n, S} same steps determining the layer 2 by using Equation 4 to 7 are repeated in order to determine the layer n.

Meanwhile, although not shown in FIG. 7, RSs whose layers are not determined in the RS layering process need link capacity determined by AMC when calculating a delay time to determine whether they are suitable for the corresponding layer. SINR should be calculated. Since the present invention assumes that each RS knows the signal strengths of other RSs, it is possible to determine the RS of the corresponding link by determining only the RS to act as an interference source.

Specifically, when r _k having no layer is determined, the RS does not use the resources received by r _k among the RSs whose layers have been determined. However, it is unclear whether the other RSs will act as an interference source according to the topology which is configured later because the topology is not completed.

The easiest approach here is to think that all possible RSs are interference sources, as shown in Figure 8 (a). This is a 'worst case' that calculates the link capacity when the link is in its worst state. However, in such a 'worst case', the algorithm can not be applied because the state that is less than the minimum MCS level in the AMC table-based calculation may come to the maximum value. In addition, if a layer is determined without considering interference to be removed through RS grouping to be described later, there is a high probability that RS belonging to a wrong layer occurs in the RS grouping result.

Therefore, in the present invention, as shown in FIG. 8 (b), the RS that satisfies the predetermined condition uses a 'reduced worst case' removed from the interference source. That is, the strength of the signal r _k T is received _RSS or more RS are thereby excluded from the interference source of r _k. This is because RSs with strong signal strengths will be physically present in the vicinity of r _k , and physically close RSs can be expected to be layered with a maximum ± 1 layer difference during the layering process. In addition, because it can expect that when r _k in the first place is not to use the resource for receiving or even with the resource r _k is the received interference from RS aggregation process to be described later is to be removed.

T _RSS is a value obtained by converting an average distance to a neighboring RS into signal strength as shown in the following equation, assuming only path loss and N N distributions.

는 중복되지 않은 RS의 커버리지이다.Where P _{Tx, RS} is the transmit power of the repeater, α is the path loss index according to the channel aspect, R _BS is the coverage of the BS,

Is coverage of non-overlapping RS.

In the layers of RSs determined through the RS layering algorithm as described above, each RS must select its own upper RS in the upper layer. A subset of RSs called clusters in one layer selects the same upper RS in the higher layer. The purpose of this RS aggregation algorithm is to determine the upper RS for each RS in the upper layer in order to minimize the effective delay. In general, exhaustive searching is so complex that the present invention uses much less complex heuristics.

The selection of a new higher RS in the RS aggregation process changes the topology formed through RS layering and thus the degree of inter-hop interference. The upper RS for the RS in the candidate H _n in order to minimize the variation of the hop-by-hop interference is limited to the RS in the H _{n-1, S} determined through the RS layered.

와 같이 주어진다. 여기서

이다.9 is a flowchart illustrating RS aggregation according to the present invention. Referring to FIG. 9, first, G = H _{n-1, S} , and the RS having the smallest SINR in the link with the upper RS among the RSs in G is selected as the test RS (TRS) (S901). That is, TRS

Is given by here

to be.

라고하면, 다음의 수학식에 의해 임시 상위 RS

와

에 속하는 각 RS q _m 의 임시 실효 지연

이 결정된다(S903).Next, the set of sub-RSs of the TRS

Speaking, the temporary upper RS by the following equation

Wow

Temporary effective delay of each RS q _m belonging to

This is determined (S903).

such that

such that

when

when

에 있는 다른 RS에 의한 결정의 효과가 고려되어야 하는데, 이는 전체 결정 절차를 너무 복잡하게 해서 구현하기가 어렵다. 따라서 본 발명에서는 다음과 같이 발견적 방법(heuristics)을 사용한다. 즉, q _m 의

보다 더 작은

를 가지는

에 의한 결정의 효과가

의 선택 절차에 고려된다. 예를 들면,

에 있는 RS들 중에서 가장 작은

를 가지는 RS는 다른 RS들의 효과를 고려하지 않고 임시 상위 RS를 고정한다(S905). 그 러나 다른

의 RS들은 앞서 선택된 RS의 결정에 따른 간섭 및 트래픽 부하를 반영하여

을 결정하고, 이중 가장 작은

를 가지는 RS가 다시

으로 선택된다. 이러한 과정을 모든

의 원소가 임시 상위 RS를 결정할 때까지 반복한다.But in the actual selection process

The effect of the decision by the other RS in 되어야 should be considered, which makes the whole decision procedure too complex and difficult to implement. Therefore, the present invention uses heuristics as follows. That is, q _m

Smaller than

Having

The effect of the decision by

Is considered in the selection procedure. For example,

The smallest of the RS in

The RS having a fixed fixed temporary upper RS without considering effects of other RSs (S905). However other

RSs reflect the interference and traffic load according to the decision of the previously selected RS.

Determined, and the double the smallest

RS with again

Is selected. All these processes

Repeat until the element at determines the temporary upper RS.

은 실제 상위 RS로 받아들여질 것이다(S907, S909). 그렇지 않으면

은 수용되지 못하고

선택 이전의 토폴로지로 복구시킨다(S911). 그런 다음 G는

로 업데이트된다. 그리고 이와 같은 선택 절차는 G에 남아 있는 모든 RS들이 없어질 때까지 반복된다(S913).If this chosen new topology reduces the effective delay compared to the previous topology, q _m

Will be accepted as the actual upper RS (S907, S909). Otherwise

Could not be accepted

Restore to the topology before the selection (S911). Then G is

Is updated to. This selection procedure is repeated until all RSs remaining in G disappear (S913).

10 and 11 are graphs showing average terminal yield and terminal service inefficiency when N = 3, respectively. 10 and 11, it can be seen that the best yield and the lowest service inefficiency can be achieved when RS layering and RS grouping according to the present invention are executed together. In particular, as can be seen from FIG. 11, 'RS layering' or 'RS aggregation' itself is a useful means to reduce co-channel interference. In addition, in the other methods except the RS layering and the RS aggregation method according to the present invention, the service unavailable performance decreases as the number of RSs increases in a large number of RSs. From this, it can be seen that the RS layering and RS grouping procedures according to the present invention can adequately handle inter-branch interference according to a large number of RSs.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be defined by the equivalents of the claims of the present invention as well as the following claims.

1 is an exemplary view showing the structure of a multi-hop relay frame

2 is an exemplary diagram illustrating a multi-hop relay frame structure when N = 4

3 is an exemplary view showing a reuse 1 / K scheme of K = 3 in a multi-hop relay system;

4 is an exemplary view showing a network configured by applying a 1 / K frame structure of K = 3.

5 is an exemplary view showing the effect of topology control in a multi-hop relay system

6 is an exemplary diagram showing hierarchical RS grouping for dynamic topology control according to the present invention.

7 is a flowchart illustrating an RS layering method according to the present invention.

8 is an exemplary view illustrating an interference source prediction method in an RS layering process according to the present invention.

9 is a flowchart illustrating an example RS aggregation method according to the present invention.

10 is a graph showing average termination yield performance when N = 3

11 is a graph showing average terminal service inefficiency performance when N = 3

Claims (22)

In the relay layering method for multi-hop relay of a cellular TDD-OFDMA system, (a) measuring the signal-to-interference and noise ratio (SINR) of the link between the repeater and the base station, selecting repeaters having the best connection with the base station to form a set of repeaters belonging to Layer 1; (b) further selecting repeaters that may be included in layer 1; (c) selecting a repeater having the best connection with the layer 1 to form a set of repeaters belonging to layer 2; (d) forming a set of repeaters which may have lower repeaters in the layer 2; And (e) additionally selecting repeaters that may be included in layer 2; And determining a repeater that will act as an interference source of the repeater whose layer is not determined, from among the relays having the determined layer. delete The repeater of claim 1, wherein the repeater to act as an interference source is determined by excluding a repeater whose strength of a signal received by the repeater whose layer is not determined from among the repeater whose layer is determined is greater than or equal to a predetermined value. Relay layering method. delete delete According to claim 1, wherein step (b), (b-1) forming a candidate set of the layer 1 with repeaters not selected in the step (a); And (b-2) additionally selected repeaters from the candidate set and included in the layer 1 that can achieve greater capacity through direct connection to the base station than through the repeaters selected in step (a) Relay layering method comprising a. 7. The method of claim 6, further comprising repeating steps (b-1) and (b-2) until no more repeaters can be included in the layer 1 in the candidate set. . delete delete delete The method of claim 1, wherein step (e) (e-1) forming a candidate set of layer 2 from the repeaters included in the layer 1 and the remaining repeaters except the repeaters selected in the step (c); And (e-2) relay repeaters capable of achieving greater capacity through repeaters belonging to the set formed in step (d) are selected from the candidate set and included in the layer 2; 12. The method of claim 11, further comprising repeating steps (e-1) and (e-2) until no more repeaters can be included in the layer 2 in the candidate set. . delete In the relay aggregation method for multi-hop relay of a cellular TDD-OFDMA system, (a) selecting a repeater having a minimum signal-to-interference noise ratio (SINR) as a test repeater in a link with a higher repeater; (b) determining a temporary upper repeater and a temporary effective delay for each repeater belonging to a set of lower repeaters of the test repeater; And (c) selecting the actual upper repeater according to the temporary effective delay for the determined temporary topology. The method of claim 14, wherein step (b) comprises: (b-1) fixing a temporary upper repeater of the repeater having the smallest temporary effective delay in the set of lower repeaters of the test repeater to which the temporary upper repeater is not fixed; (b-2) repeating, by the repeaters of the set of lower repeaters of the test repeater, to which the temporary upper repeater is not fixed, reflecting the interference and traffic load caused by the repeater to which the temporary upper repeater is fixed; And (b-3) steps (b-1) and (b-2) until the temporary upper repeater is fixed for all repeaters belonging to the set of lower repeaters of the test repeater in which the temporary upper repeater is not fixed; Relay grouping method comprising the step of repeating the steps. delete The method of claim 14, wherein step (c) comprises: If the new topology determined in step (b) has a reduced effective delay compared to the topology of step (a), selecting the temporary upper repeater determined in step (b) as the actual upper repeater; And Restoring to the topology of step (a) if the new topology determined in step (b) does not reduce the effective delay compared to the topology of step (a). A dynamic topology control method for multi-hop relay in a cellular TDD-OFDMA system, A resource reuse step in which subzones of the K (K≥2) divided relay zones are reused in another layer; A relay layering step of placing the relays (RSs) in layers of another layer; And Relay grouping step of finding a set of repeaters (RS) connected to the same upper repeater (RS) of the upper layer, The relay layering step includes the steps of the relay layering method according to any one of claims 1, 3, 6, 7, and 11 to 12, The relay grouping step comprises steps of the relay grouping method according to any one of claims 14, 15 and 17. The method of claim 18, wherein the resource reuse step, Dividing the relay zone of the multi-hop relay frame into K (K ≧ 2) subzones; And And wherein the divided sub zones are reused in different layers every K (K≥2) hops. delete delete delete

Images