KR20170083777A - Method and Apparatus for Public safety users priority based time and energy efficient D2D discovery in 3GPP LTE-A system - Google Patents

Abstract

A public security user priority based time and energy efficient D2D search method and apparatus in the 3GPP LTE-A system proposed in the present invention are presented. In the 3GPP LTE-A system proposed in the present invention, the public safety user priority based time and energy efficient D2D search method includes placing DPUs and DNPUs in a network coverage area and initializing parameters, based on public safety user priorities Dynamically adjusting the DPUs according to the number of DPUs, allocating search resource blocks for the DPUs and the DNPUs, and allocating resources among the DPUs using a switching scheme according to the degree of competition for channel access .

Description

FIELD OF THE INVENTION [0001] The present invention relates to a 3GPP LTE-A system and a public safety user priority based time and energy efficient D2D detection method and apparatus for 3GPP LTE-

The present invention relates to a priority-based time and energy efficient device search method and apparatus for public safety users for ProSe in a 3GPP LTE-A system.

The popularity of the smartphone and the concept of the Internet (IoT) are fueling an increase in the total data rate for next generation mobile communications (5G) systems. In order to achieve this data rate, a major paradigm change in conventional homogeneous macrocells, which is an evolutionary form in an eNodeB (eNodeB) based network architecture, is required. D2D communications have been identified in the 3G Partnership Project (3GPP) Release 12 as a new driver for wireless communications and mobile markets for traffic interruption from traditional overloaded eNB-based cellular network structures. In the background of 3GPP's adoption of D2D, the popularity of proximity-based services (ProSe) for social networking applications, context aware applications, high spectrum efficiency and low latency applications, improved user experience, There are various synchronization factors such as an enabler. Another motive for integrating D2D with LTE-A comes from the urgent need to provide public protection and disaster relief (PPDR) in disaster situations and in mission-critical situations. Currently, ad-hoc network-based technologies such as WiFi or Bluetooth provide D2D communication capabilities in the market. However, since this technique operates in unauthorized bands, interference control is impossible, quality of service (QoS) can not be guaranteed, and it is less secure. To improve this situation, the D2D search cellular architecture has different manual operation levels to combine the advantages of ad-hoc and coordinated networks. The choice of manual operation level depends on two conditions. The first is a D2D coverage scenario, such as in-network coverage, partial network coverage, and out-of-network coverage scenarios. The second is the user's service requirements such as QoS, latency, public safety (PS) applications and use cases, and interference conditions.

Device-to-device discovery is a key element in providing proximity-based services to the third-generation partnership project LTE-A (long-term evolution advanced) for public safety and overall LTE scenarios. The placement of the D2D network results in severe co-channel interference between conventional cellular users and D2D users. The present invention proposes a device search resource allocation (TEECR-DDRA) scheme that efficiently and competitively resolves time and energy in order to improve the search success rate of D2D users by reducing collision between users. In addition, the proposed TEECR-DDRA scheme has the ability to determine the priority of PS users to meet QoS and latency requirements. Furthermore, ALOHA with energy sensing and multiple channels can be used to increase the probability of a non-PS user's search success. This feature helps to reduce the PS user's search time under disaster scenarios and minimizes the number of beacon retransmissions to reduce non-PS user energy consumption. System-level simulations show that the proposed TEECR-DDRA scheme performs very well in a tightly deployed D2D network. Compared to the conventional random access scheme, the proposed scheme almost doubles the search range and improves the success rate for the search of the D2D user.

1 is a diagram for explaining another type of operation control level-based D2D search in a 3GPP ProSe LTE-A system.

As can be seen in Figure 1, in 3GPP Release 12, D2D discovery for PS public safety users (UEs) and non-public safety users (NPS UEs) is only possible in the current in-network coverage scenario. Therefore, it is necessary to focus only on in-network coverage deployment scenarios for the PS UE 130 and non-PS UE 120 arrangements. For example, in the case of in-network coverage deployment scenarios, two approaches are possible. In a full-passive control 170 link setup or UE-specific type 2 search scheme 180, the operator has full control over the search phase in the radio resource allocation and other mechanisms, QoS can also be guaranteed. In the partial-manual control 160 scenario or the non-UE specific type 1 search method 190, as shown in FIG. 1, a radio resource is initially allocated to a user group by an operator to acquire resources for searching among users There will be competition for this. The partial-passive control situation has the advantage of less feedback, less overhead and less complexity compared to a fully manual control situation, but it has a lot of interference. Thus, the Type 1 lookup scheme is an optimal choice for non-PS users, as the number of UEs required by the D2D service will be very high in the future. Furthermore, for users who require radio resource priorities in a disaster situation, the Type 2 search method will be a better choice.

According to the prior art, one of the major design challenges for D2D search is radio resource allocation, where each device selects one of the search resources to transmit a search signal. Most of the existing radio resource allocation solutions such as split frequency reuse, power control scheme, and cooperative scheduling scheme are based on the conventional eNB 110 structure. These solutions are unsuitable for the D2D scenario because they only fit under the context of a fully-manual control scenario. Similarly, recent research on numerous D2Ds, such as interference-aware resource allocation schemes, joint scheduling and resource allocation, and distributed power control, focuses on radio resource management associated with D2D communications. However, relatively little attention has been given to D2D search, a key element in providing new access-based services.

The main design goals of the D2D discovery approach are energy efficiency, long search range, QoS enhancement, and suitability for both PS and non-PS scenarios. In order to achieve these goals, a location-based search method, an energy efficient search considering neighboring regions, a D2D search method based on inter cell interference coordination, a D2D search for proximity service, and a conflict solution for D2D search Method, and D2D communication for public safety. Although some of the proposed solutions save energy, suggest new search structures, are simple and time-efficient, they cause many problems. For example, an energy efficient search and an intercell interference coordination (D2D) search scheme considering neighboring regions increases the number of devices to be searched by avoiding collision and interference, taking into consideration the location information of the user, Does not agree with the convention in 3GPP. Thus, these schemes are not suitable for future D2D search schemes based on 3GPP LTE-A. Even though the frame structure of the collision-resolving scheme for D2D search conforms to the 3GPP standard, it will not be suitable for retrieving a large number of devices because it will have some specific resources for beacon collision detection. In addition, most of the proposed schemes focus on random channel access that causes more collisions, resulting in more energy consumption due to retransmissions. Also, since all of the proposed schemes individually determine the resource allocation problem for the PS users and the non-PS users, the PS users in the resource allocation are inherently static since they are not given priority.

SUMMARY OF THE INVENTION The present invention provides a device search resource allocation (TEECR-DDRA) method and apparatus for efficiently and competitively resolving time and energy, capable of improving the search success rate of D2D users by reducing collision between users, .

In one aspect, the public safety user priority-based time and energy efficient D2D search method in the 3GPP LTE-A system proposed by the present invention is implemented in the network coverage area of DPUs (D2D PS Users) and DNPU (D2D Non-PS Users) Allocating search resources blocks for the DPUs and DNPUs based on public safety user priorities and dynamically adjusting according to the number of DPUs, And allocating resources between the DPUs using a switching scheme according to the present invention.

Wherein the step of allocating the search resource blocks for the DPUs and the DNPUs by dynamically adjusting according to the number of the DPUs is based on the number of the DPUs, If the number of search resource blocks is larger, the search resource block for the DPUs is acquired in the first search cycle.

In the 3GPP LTE-A system, the public safety user priority based time and energy efficient D2D search method further comprises performing the D2D search according to the SINR for performing the D2D search.

The performing the D2D search according to the SINR for performing the D2D search may include performing the D2D search when the SINR for performing the D2D search is less than or equal to a predetermined threshold value, If it is equal to or greater than the predetermined threshold value, the search resource block for the DPUs is acquired in the second search cycle.

Wherein the step of allocating the search resource blocks for the DPUs and the DNPUs by dynamically adjusting according to the number of the DPUs is based on the number of the DPUs, If the number of search resource blocks is smaller, obtains all available search resource blocks for the DPUs in the first search period, the remaining unscheduled DPUs send an emergency connection request to the eNB, and in the second search period, Thereby securing the search resource block for DPUs.

At this time, the DPUs compete to secure the search resource block using the MCALOHA method or the MCALOHA-ES method in the second search period.

Wherein the step of allocating resources among the DPUs using a switching scheme according to the degree of competition for the channel access comprises: if the degree of competition for the channel access is equal to or greater than a predetermined threshold, -System switched.

In another aspect, in the 3GPP LTE-A system proposed by the present invention, a public safety user priority based time and energy efficient D2D search apparatus includes an initialization unit for placing DPUs and DNPUs in a network coverage area and initializing parameters, A search resource block allocation unit based on public safety user priority and dynamically adjusting according to the number of DPUs and allocating search resource blocks for the DPUs and the DNPUs; And allocating resources between the DPUs.

The search resource block allocation unit compares the number of search resource blocks with the number of DPUs and acquires the search resource block for the DPUs in a first search period when the number of search resource blocks is larger.

In the 3GPP LTE-A system, the public safety user priority based time and energy efficient D2D search apparatus further comprises a search unit for performing the D2D search according to the SINR for performing the D2D search.

Wherein the search unit performs the D2D search when the SINR for performing the D2D search is equal to or less than a predetermined threshold and if the SINR for performing the D2D search is equal to or greater than a predetermined threshold value, Thereby securing the search resource block for the search resource block.

The search resource block allocation unit compares the number of search resource blocks with the number of DPUs to reserve all available search resource blocks for the DPUs in a first search period when the number of search resource blocks is smaller, The remaining DPUs that have not been transmitted transmit the emergency connection request to the eNB and acquire the search resource block for the DPUs in the second search cycle.

At this time, the DPUs compete to secure the search resource block using the MCALOHA method or the MCALOHA-ES method in the second search period.

The switching unit switches the channel access protocol from MCALOHA to MCALOHA-ES to avoid contention if the degree of competition for the channel access is greater than or equal to a predetermined threshold.

According to embodiments of the present invention, the proposed TEECR-DDRA scheme has the ability to determine the priority of a PS user to meet QoS and latency requirements. In addition, ALPHA with energy sensing and multiple channels can be used to increase the probability of a non-PS user's search success. It also helps to reduce the search time of PS users under disaster scenarios and minimizes the number of beacon retransmissions, thereby reducing energy consumption of non-PS users. System-level simulations show that the proposed TEECR-DDRA scheme performs very well in a tightly deployed D2D network. Compared to the conventional random access scheme, the proposed scheme almost doubles the search range and improves the success rate for the search of the D2D user.

1 is a diagram for explaining another type of operation control level-based D2D search in a 3GPP ProSe LTE-A system.
2 is a scenario for D2D for PUs and NPUs in the 3GPP LTE release according to one embodiment of the present invention.
3 is a flowchart illustrating a public security user priority based time and energy efficient D2D search method in a 3GPP LTE-A system according to an embodiment of the present invention.
4 is a diagram illustrating a D2D search uplink frame structure of PUs and NPUs according to an embodiment of the present invention.
5 is a detailed view illustrating a device search frame structure having a PUCCH showing dynamic adjustment of search resources considering DPUs priorities according to an embodiment of the present invention.
6 is a diagram illustrating a configuration of a public security user priority based time and energy efficient D2D search apparatus in a 3GPP LTE-A system according to an embodiment of the present invention.
7 is a diagram illustrating a radio access network shared between NPUs and PS in ProSe LTE according to an embodiment of the present invention.
8 is a diagram illustrating a system level simulation environment for performance verification according to an embodiment of the present invention.
9 is a graph showing the number of users retrieved according to an embodiment of the present invention.
10 is a graph showing search distances of users according to an embodiment of the present invention.
FIG. 11 is a graph illustrating a search coverage success rate of users according to an embodiment of the present invention.
12 is a graph showing a search range failure rate of a user according to an embodiment of the present invention.

In order to solve the above-described problems, the present invention uses TEACHR-DDRA (Device Search Resource Allocation (TEECR-DDRA), which efficiently and competitively resolves time and energy, using selective energy sensing and multi-channel ALOHA for ProSe of 3GPP LTE- Method. Compared to the solutions presented in the prior art, the main advantages of TEECR-DDRA are: 1) dynamic reconciliation of discovery resources (DR) by considering the number and priority of PS users sending connection requests for device discovery And leave it. 2) If the counter exceeds a certain threshold to avoid beacon collisions, or if a non-PS user fails to access the channel after some attempt, the MCALOHA-ES concept is used and the result is that the channel approach is random access MCALHOHA) to Energy Sensing Random Access (MCALOHA-ES). The centralized D2D search method based on MCALOHA-ES has not been proposed in the prior art. This avoids collisions, helps to reduce time and energy consumption, and does not waste energy in beacon retransmissions. 3) Since the proposed TEER-DDRA scheme is designed according to 3GPP standards, it can be easily applied to 3GPP LTE-A based system without any modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a scenario for D2D for PUs and NPUs in the 3GPP LTE release according to one embodiment of the present invention.

Consider in-network coverage scenario 1D in which multiple cells are deployed in the four possible deployment scenarios shown in FIG. In this scenario, all the devices that need to be searched are placed in their respective network coverage areas. A detailed description of the scenario is summarized in Table 1.

<Table 1>

D2D search is the initial step for D2D communication. A UE that is to be discovered by other users in a close transmission will send a beacon containing identification (ID) information to the assigned DR (discovery resource). Other UEs that will perform a scan will scan for DR during the beacon transmission period. In order to successfully decode the received beacon, the signal to interference and noise ratio (SINR) must be greater than or equal to a certain threshold.

By a half-duplexing constraint, the UE transmitting the beacon can not scan the DR to search for other neighboring UEs. The D2D search is classified into the type 1 search method and the type 2 search method as described above. In a type 2 search scheme, search resources, power allocation for DR, and other mechanisms are mainly controlled by the eNB. In the type 1 search scheme, initially DR is occupied by the eNB, but there is a contention between users to access the resource. Thus, the Type 2 search scheme is suitable for a small number of users due to the many signaling overheads and complexity, while the Type 1 search scheme is suitable for ultra-dense network (UDN) deployments. For the purposes of the present invention, we consider Type 2 retrieval schemes for PS users (PUs) and Type 1 retrieval schemes for non-PS users (NPUs) for two different UE types.

3 is a flowchart illustrating a public security user priority based time and energy efficient D2D search method in a 3GPP LTE-A system according to an embodiment of the present invention.

In the proposed 3GPP LTE-A system, the public safety user priority based time and energy efficient D2D search method places DPUs and DNPUs in the network coverage area and initializes the parameters (ie T = 1, DNPU _i _C = 0) Allocating a search resource block for the DPUs and the DNPUs based on a public safety user priority and dynamically adjusting according to the number of DPUs and using a switching method according to the degree of competition for channel access And allocating resources between the DPUs.

Wherein the step of allocating the search resource blocks for the DPUs and the DNPUs by dynamically adjusting according to the number of the DPUs is based on the number of the DPUs, If the number of search resource blocks is greater, the search resource block for the DPUs is acquired in a first search period (i.e., T = 2).

In the 3GPP LTE-A system, the public safety user priority based time and energy efficient D2D search method further comprises performing the D2D search according to the SINR for performing the D2D search.

The performing the D2D search according to the SINR for performing the D2D search may include performing the D2D search when the SINR for performing the D2D search is less than or equal to a predetermined threshold value, If it is greater than or equal to the predetermined threshold, the search resource block for the DPUs is acquired at the second search period (i.e., T = 3).

Wherein the step of allocating the search resource blocks for the DPUs and the DNPUs by dynamically adjusting according to the number of the DPUs is based on the number of the DPUs, If the number of search resource blocks is smaller, obtains all available search resource blocks for the DPUs in the first search period, the remaining unscheduled DPUs send an emergency connection request to the eNB, and in the second search period, Thereby securing the search resource block for DPUs. At this time, the DPUs compete to secure the search resource block using the MCALOHA method or the MCALOHA-ES method in the second search period.

Wherein the step of allocating resources among the DPUs using a switching scheme according to the degree of competition for the channel access comprises: if the degree of competition for the channel access is equal to or greater than a predetermined threshold, -System switched.

에서 더 먼 거리에서, 더 적은 에너지를 소모하면서, D-UE

에 의해 검출되고 검색되는 사용자들의 수를 증가시키는 것이 주요 목표이다. 따라서, 이러한 모든 목표들을 달성하기 위해, MCALOHA-ES를 사용한 TEECR-DDRA 방식을 제안한다. 이 방식은 DRs를 사용자의 우선순위에 따라 두 부분으로 나누어 동적으로 조정하는 능력을 가지고 있다: 1) 높은 우선순위의 DPUs를 위한 비경쟁-기반 별도 자원의 예약과 2) DNPUs를 위한 경쟁-기반 자원. 그러나, 이 방식은 주위의 D-UEs를 스마트하게 검색하는데 도움을 주는 효율적인 MCALOHA-ES 방식을 사용함으로써 경쟁을 피하거나 줄일 수 있다. 제안된 방식의 다른 특징은 랜덤 액세스 MCALOHA 방식에서 non-랜덤 MCALOHA-ES로의 스위칭 개념이다. 한 방식에서 다른 방식으로 스위칭하기 위해, 카운터의 개념이 D-UE 측에 도입되었다. 카운터가 어떤 한계를 초과 할 경우, D-UE는 충돌을 해결하기 위해 채널 액세스 프로토콜을 스위칭한다. 따라서, 두 가지 채널 액세스 방식의 이점을 결합하는데 도움이 되며, 경쟁을 줄이는 데도 도움이 되고, 에너지를 적게 소비함으로써 짧은 시간 내에 검색이 된다. 제안된 TEECR-DDRA 방식의 주요 단계는 아래와 같다.Conventional communication techniques in cellular network architectures are aimed at high data rates, improved link reliability, and reduced power failure rates. For D2D search, considering the priority of the DPUs, in a shorter time, with less beacon retransmission, the D-UE

Lt; RTI ID = 0.0 &gt; D-UE &lt; / RTI &gt;

To increase the number of users to be detected and retrieved. Therefore, to achieve all of these goals, we propose a TEECR-DDRA scheme using MCALOHA-ES. This approach has the ability to dynamically tune DRs into two parts according to user priorities: 1) reservation of non-contention-based discrete resources for high priority DPUs and 2) contention-based resources for DNPUs . However, this approach can avoid or reduce competition by using an efficient MCALOHA-ES scheme that helps smartly search for nearby D-UEs. Another feature of the proposed scheme is the concept of switching from random access MCALOHA to non-random MCALOHA-ES. To switch from one mode to the other, the concept of a counter was introduced on the D-UE side. If the counter exceeds a certain limit, the D-UE switches the channel access protocol to resolve the conflict. Therefore, it helps to combine the advantages of the two channel access schemes, helps to reduce competition, and searches in less time by consuming less energy. The main steps of the proposed TEECR-DDRA method are as follows.

First, DPUs and DNPUs placement and parameter initialization are performed within the network coverage area (310). Here, the parameters may include the search period, the number of DPUs, the number of DNPUs, the number of DRs, DNPU _i _C. The number of DPUs = {1, 2, ..., M}, the number of DNPUs = {M + 1, M + 2, ..., N}, the number of DRs = {1, 2, ..., P }, Initializing the search cycle for DNPUs T = 1, DNPU _i _C = 0, where i ∈ {number of DNPUs}.

At this stage, DPUs and DNPUs are placed in the network coverage area using macro scenario 3. Scenario 3 is suitable for public safety situations and is a common scenario, with a total of 125 UEs deployed per sector. 30% of the total UEs are the number of DPUs, and the rest are DNPUs.

4 is a diagram illustrating a D2D search uplink frame structure of PUs and NPUs according to an embodiment of the present invention.

후 마다 주기적으로 점유되고, 주파수 도메인은

자원 블록들의 자원과

서브프레임의 시간 도메인 자원들을 10MHz LTE 시스템 대역폭에서 점유한다. A D2D search frame structure according to an embodiment will be described. It is assumed that 3GPP uses LTE uplink (UL) radio resources for D2D search. Thus, in the present invention, the D2D UE (D-UE) utilizes uplink resources to search for neighboring devices. To ensure the performance of the D2D search,

The frequency domain is periodically occupied

Resources of resource blocks

Occupies the time domain resources of the subframe in the 10MHz LTE system bandwidth.

As shown in FIG. 4, the remaining resources are provided to conventional cellular UEs (CUEs) connected to the eNB for UL transmission. In the proposed scheme, since we have PRs and NPUs, we divide the DR into two parts, dynamically adjusted to the number of PUs, while sending the emergency connection request to the eNB.

는 검색 슬롯 동안에 사용 가능한 DRs에서 수신된 에너지 레벨을 고려하고, 최소로 수신된 에너지에 기반하여 아래와 같이

를 선택한다.There are two classes of D2D search resource allocation in 3GPP ProSe: random resource allocation and sensing-based resource allocation. In random resource allocation, all devices in the system randomly select their DRs for beacon transmission in the available DRs. This has the benefit of low latency and low feedback complexity, but it also has a greater opportunity cost for collisions between users transmitting beacons while accessing the same channel at the same time. On the other hand, in the sensing-based search resource allocation,

Lt; RTI ID = 0.0 &gt; DRs &lt; / RTI &gt; that are available during the search slot, and based on the minimally received energy,

.

(1)

(One)

Sensing-based resource allocation has less potential for collisions between users, but has high feedback complexity. Therefore, in order to combine the advantages of random channel allocation and sensing based channel allocation, both resource allocation schemes are utilized based on the number of failed beacon transmissions. In the present invention, multi-slotted ALOHA (MCALOHA) is used for random resource allocation and MCALHOA (MCALOHA-ES) is added to smart D2D search for sensing-based resource allocation.

In the step of allocating search resource blocks for the DPUs and the DNPUs based on the public safety user priority of the proposed method and dynamically adjusting according to the number of DPUs, during the resource allocation step, And the priority is given by the eNB. In other words, resources can be dynamically adjusted according to the number of DPUs while sending an emergency connection request. If the number of DPUs is greater than the number of DNPUs, during the j &lt; th &gt; subframe of the search period T, resources for the DNPU will not be secured and DNPUs will be provided in the next (next) search cycle. After the resources are acquired, a round robin scheduler is used to allocate resources among the DPUs. MCALOHA and MCALOHA-ES are used to allocate resources and avoid competition.

First, in the current search cycle, the DPUs send Emergency request messages (ERMs) to the eNB for allocation of EDRs (321). Next, the number of DRs and the number of DPUs are compared (330). If the number of DRs is greater than the number of DPUs, the eNB obtains R EDRs for the DPUs, and ( PR ) DRBs for the NPUs remain in the next DTP (331). Then, the process moves to a step of allocating resources among the DPUs using a switching scheme according to the degree of competition for channel access (340).

If the number of DRs is less than the number of DPUs, the eNB obtains 332 all available DRs for the DPUs at the next DTP (e.g., T = 2). The remaining unscheduled DPUs send the ERMs back to the eNB at the next DTP and then acquire 351 the EDRs at the DTP (e.g., T = 3). DNPUs then compete for DRBs in the DTP by using the MCALOHA / MCALOHA-ES scheme (352). In addition, changes to _{T = T + 1, DNPU i} _C = DNPU i _C +1 (353).

5 is a detailed view illustrating a device search frame structure having a PUCCH showing dynamic adjustment of search resources considering DPUs priorities according to an embodiment of the present invention.

로 표시된다. 이 세트는 UEs의 총 수인 N으로 이루어지며, 이것은 D2D PS UEs(DPUs)와 D2D Non-PS UEs(DNPUs)를 포함하고, 아래와 같이 나타낼 수 있다.In LTE-A, a physical resource block (PRB) is defined as a group of 12 consecutive subcarriers in the frequency domain, while a subframe or transmit time interval (TTI) Lt; RTI ID = 0.0 &gt; OFDM &lt; / RTI &gt; Due to the fixed size of the PRBs, there are 50 PRBs for a system bandwidth (BW) of 10 MHz. For a D2D search, each UE needs at least two PRBs to send and receive beacons. As shown in FIG. 5, six of the 50 PRBs are required to transmit the physical uplink control channel (PUCCH) at 10 MHz BW, since the D2D search uses UL resources, while the remaining 44 The PRBs are DRs available for transmitting and receiving beacons. It is assumed that all D-UEs use scenario 1D in which all UEs are in network coverage and are synchronized with it. The synchronization criterion is obtained from the eNB download link (DL) transmission. Synchronous retrieval has the advantage of less energy consumption, and the D-UE wakes up only for a predetermined search time as it uses the search for synchronization. Performance statistics such as the number of detected UEs and the successful retrieval probability of D-UEs are collected only from the ROI of interest. In each sector, the set of indices for UE u associated with the D2D search is

. This set consists of the total number of UEs, N, which includes D2D PS UEs (DPUs) and D2D Non-PS UEs (DNPUs), and can be expressed as:

(2)

(2)

And by using a switching method according to the competition for access to the channel in the step of allocating resources among the DPUs comparing the value of the pre-defined W and DNPU _i _C (340).

의 실패 횟수가 미리 정의된 W의 값을 초과하게 되면, 채널 액세스 프로토콜은 경쟁을 피하기 위해 MCALOHA에서 MCALOHA-ES로 스위칭된다(342). 다시 말해, DNPUs는 MCALOHA 방식에 의해 DRs를 선택한다. 그 결과, 불필요한 재전송 에너지가 감소한다. In the presence of severe competition for channel access, the switching concept is utilized to provide diversity for channel access to DNPUs. In other words, DUE

The channel access protocol is switched from MCALOHA to MCALOHA-ES (342) to avoid contention. In other words, DNPUs select DRs by the MCALOHA method. As a result, unnecessary retransmission energy is reduced.

의 실패 횟수가 미리 정의된 W의 값보다 작은 경우, 해당 DNPUs는 MCALOHA-ES 방식에 의해 DRs를 선택한다(341). On the other hand, DUE

If the number of failures is less than the predefined value of W, the corresponding DNPUs selects DRs by the MCALOHA-ES scheme (341).

Next, the value of SINR _i is compared with a predetermined threshold value SINR _threshold (360). If the value of SINR _i is greater than a predetermined threshold SINR _threshold , the UEs can be successfully retrieved.

On the other hand, if the value of SINR _i is smaller than the predetermined threshold SINR _threshold , unsuccessful DNPUs acquire DRs at the next DTP (362). In addition, changes to _{T = T + 1, DNPU i} _C = DNPU i _C +1 (363).

)는 검색 주기 T의 j 번째 서브프레임동안 검색 beacon을 동시에 전송하는 K UEs를 제외한 N UEs로 구성된다. 따라서, UE u에 대한 검색 가능한 UEs 세트는 아래와 같이 표현될 수 있다:In the present invention, because of semi-double constraints, the searchable target UEs (

) Consists of N UEs except K UEs that simultaneously transmit the search beacon during the jth subframe of the search cycle T. [ Thus, the set of discoverable UEs for UE u can be expressed as: &lt; RTI ID = 0.0 &gt;

(3)

(3)

이거나 수신기

일 수 있고, 여기서

이다. 만약 사용자

에서 수신 SINR(

)이 규정된 SINR 임계 값(

)보다 더 크다면, UE

는

에 의해 검색되는 것으로 여겨지며, 여기서

인 값은 시뮬레이션에 기반하여 선택된다. 따라서, DR d 상에서 UE

로부터 UE

에 전송된 beacon의 SINR은 아래와 같다:During the search period,

Or receiver

Lt; / RTI &gt;

to be. If the user

Lt; RTI ID = 0.0 &gt; SINR

) &Lt; / RTI &gt; is the prescribed SINR threshold (

), The UE

The

, &Lt; / RTI &gt; where &lt; RTI ID =

Is selected based on the simulation. Therefore,

From UE

The SINR of the beacon transmitted to the base station is:

(4)

(4)

은

의 전송 전력이며,

은 j 번째 서브프레임 동안의 PRB 상에서

와

사이의 채널 이득이다. 이웃하는 D-UEs로 부터의 간섭은

와 같이 나타내며, 반면에 노이즈 전력은

와 같이 주어진다.here,

silver

Lt; / RTI &gt;

Lt; / RTI &gt; on the PRB for the j &lt;

Wow

Lt; / RTI &gt; The interference from the neighboring D-UEs

, While the noise power is expressed as

As shown in Fig.

The D2D search system for DNPUs can not be centrally controlled because there is no coordination between D-UEs or signaling from eNBs during the search process. In addition, since there are many DNPUs using the same PRBs at the same time, collisions or interferences that cause deterioration in signal quality occur.

가 확률 p로 비콘을 전송할 수 있으며, 확률

로 다른 비콘들을 수신한다. 만약 두 개의 D-UE들이 동시에 동일한 DR로 beacon들을 전송한다면 충돌이 발생할 것이다.In the proposed D2D search system, during each search period T, each D-UE

Can transmit a beacon with probability p, and probability

To receive different beacons. If two D-UEs transmit beacons in the same DR at the same time, a collision will occur.

가 이웃하는 N개의 D-UEs들 중 근접

를 검색할 수 있는 확률은 아래와 같이 계산된다:Therefore, during the G search period

RTI ID = 0.0 &gt; D-UEs &lt; / RTI &gt;

Is calculated as follows: &lt; RTI ID = 0.0 &gt;

(5)

(5)

Thus, the probability of retrieving the maximum number of D-UEs is as follows:

(6)

(6)

Finally, from equation (6), we conclude that for a large number of users N in the D2D search system, the search time will increase due to more collisions resulting in beacon retransmissions.

The channel model represents the propagation loss that occurs when a signal travels from the transmitter to the receiver. The general equation for modeling the channel gain (G) is as follows. :

G (dB) = AG-PL-Shd-F, (7)

이다. 송신기로부터 수신기로의 경로 손실(PL)은 D-UE들 사이의 거리 또는 eNB와 CUE 사이의 거리에 기인한다. eNB와 연결된 UEs의 PL을 계산하기 위해서, 도시 지역 모델이 고려되었으며 아래와 같이 계산된다. : Here, the antenna gain (AG) of the D-UE and the CUEs is determined by using an omni-directional antenna

to be. The pathloss (PL) from the transmitter to the receiver is due to the distance between D-UEs or the distance between eNB and CUE. To calculate the PL of the UEs connected to the eNB, an urban area model is considered and calculated as follows. :

PL (dB) = 15.3 + 37.6 log ₁₀ (R), (8)

은 eNB와 CUEs 사이의 거리(meter)이다. D-UE

와 D-UE

사이의 PL을 계산하기 위해 가시선(line-of-sight) WINNER+B1 케이스가 사용되었으며, 아래와 같이 표현될 수 있다.:here,

Is the distance between the eNB and the CUEs. D-UE

And D-UE

The line-of-sight WINNER + B1 case is used to calculate the PL between the two, which can be expressed as:

PL (dB) = 35.4 + 22.7 log ₁₀ (R ₁ ), (9)

은 D-UE

와 D-UE

간의 거리(meter)이다. 식 (7)에서, 그림자(Shd)는 UEs와 eNB/UEs 간의 경로에 존재하는 장애물들에 의해 발생한다. 이는 0dB의 평균과 XdB의 표준편차를 갖는 로그-정규분포로 모델링 된다. 즉, 서로 다른 채널 모델들은 각기 다른 X 값들을 가진다.here,

D-UE

And D-UE

Is the distance between the two. In equation (7), the shadow ( Shd ) is caused by obstacles in the path between the UEs and the eNB / UEs. This is modeled as a log-normal distribution with an average of 0 dB and a standard deviation of XdB. That is, different channel models have different X values.

Fast fading (F) is the result of a constructive and non-constructive combination of randomly delayed, reflected, scattered, and diffracted signal components. This type of fading is relatively fast and is responsible for short-term signal variations that can occur when UEs or reflectors travel a short distance. A pedestrian-B (PedB) channel model was used to model fast fading.

LTE-A is strongly considered as a candidate for a PS network, and many emergency services are currently operating in LTE environments. For example, Motorola and other professional PPDR organizations tested the suitability of PS LTE to deliver video and other information using a drones at the central control station at the scene of the accident. This information is then distributed to PS teams, such as police, fire departments, and ambulance services, to prepare for accidents. In this part, it is required to develop a system that is very robust and can address the specific communication needs of emergency services. A key advantage of using LTE for PS networks is the ability to manage wireless access efficiently and centrally, taking into account the priority, latency, and QoS requirements of emergency users. To improve this capability of PS LTE, D2D and PreSe are strongly considered candidates for PS LTE networks. Therefore, it is necessary to investigate the effect of D2D communication on the performance improvement of PS LTE. There are two possible types of D2D scenarios for improving the performance of PS LTE: The first scenario is a special case requiring separate spectrum or radio resources for DPUs. On the other hand, another scenario is that DPUs share spectrum such as CUEs and DNPUs, but this causes conflicts between users. The second scenario is more realistic and practical: Scheduling resources for DPUs is unavailable until an emergency occurs, resulting in spectral waste. Therefore, it is assumed that DPUs reuse the same spectrum as CUEs. To prevent conflicts occurring here, PS users on a shared network need special priorities in resource allocation during critical situations (eg, disaster or scheduled events such as the Olympics and the World Cup).

In order to prioritize urgent services for DPUs in commercial mobile networks, there must be a solution that limits the amount of connection attempts and allows priority access for high priority users, including emergency response. There are two main mechanisms for providing a high priority to the user in terms of resources: the first is the aspect of resource control for accessing the air interface, and the other mechanism is the aspect of resources for service level priorities. Since the problem is related to D2D discovery, rather than communication, it will prioritize networks based on air interface access rather than service level priorities. Service level priorities will be discussed in subsequent studies on D2D communications.

The purpose of giving wireless access priority to a specific user is to provide services to an emergency user. Broadcast messages should be available on a cell-by-cell basis that indicates the rating or category of subscribers whose network access is prohibited. The use of this feature allows the network operator to avoid overloading the access channel under critical circumstances. This does not mean that access control is used under normal operating conditions. To allocate resources, users are classified based on their priority, and all UEs belong to one of 10 randomly assigned classes (defined as 0 to 9 access classes) for commercial users. The class number is stored in the Universal Subscriber Identity Module (USIM). In addition, UEs belong to one or more of five special categories (11 to 15 classes), which are also stored in the USIM. A brief summary of each class of access describing the cause of the establishment of the radio link and its priority is given in Table 2.

<Table 2>

PS users in the special category are further subdivided as follows. For example, PS priority 1: management's leadership and policy-makers; PS Priority 2: Disaster response and military command and control; PS Priority 3: Public health, safety, and law enforcement orders; PS Priority 4: Public Services / Utilities and Public Welfare; PS Priority 5: Disaster Recovery (eg, National Telecommunications System). Details of the services included in each class of the special category are provided in Table 3.

<Table 3>

6 is a diagram illustrating a configuration of a public security user priority based time and energy efficient D2D search apparatus in a 3GPP LTE-A system according to an embodiment of the present invention.

In the 3GPP LTE-A system, the public safety user priority based time and energy efficient D2D search apparatus 600 includes an initialization unit 610, a search resource block allocation unit 620, a switching unit 630, and a search unit 640 .

The initialization unit 610 places the DPUs and the DNPU in the network coverage area and initializes the parameters. Here, the parameters may include the search period, the number of DPUs, the number of DNPUs, the number of DRs, DNPU _i _C. The number of DPUs = {1, 2, ..., M}, the number of DNPUs = {M + 1, M + 2, ..., N}, the number of DRs = {1, 2, ..., P }, Initializing the search cycle for DNPUs T = 1, DNPU _i _C = 0, where i ∈ {number of DNPUs}.

At this time, DPUs and DNPUs are placed in the network coverage area using the urban macro scenario 3. Scenario 3 is suitable for public safety situations and is a common scenario, with a total of 125 UEs deployed per sector. 30% of the total UEs are the number of DPUs, and the rest are DNPUs.

The search resource block allocation unit 620 allocates search resource blocks for DPUs and DNPUs based on the public safety user priority and dynamically adjusting according to the number of DPUs.

The search resource block allocation unit 620 compares the number of search resource blocks with the number of DPUs to determine a search resource block for DPUs in a first search period (i.e., T = 2) .

The search resource block allocation unit 620 allocates resources from the DPUs to the eNBs while allocating resources during the resource allocation step.

The search resource block allocation unit 620 compares the number of search resource blocks with the number of DPUs and acquires all available search resource blocks for DPUs in the first search period when the number of search resource blocks is smaller. The remaining unscheduled DPUs send an emergency connection request to the eNB and acquire a search resource block for the DPUs in a second search cycle (i.e., T = 3). At this time, the DPUs compete in the second search cycle to secure the search resource block using the MCALOHA method or the MCALOHA-ES method.

In other words, resources can be dynamically adjusted according to the number of DPUs while sending an emergency connection request. If the number of DPUs is greater than the number of DNPUs, during the j &lt; th &gt; subframe of the search period T, resources for the DNPU will not be secured and DNPUs will be provided in the next (next) search cycle. After the resources are acquired, a round robin scheduler is used to allocate resources among the DPUs. MCALOHA and MCALOHA-ES are used to allocate resources and avoid competition.

First, in the current search cycle, DPUs send ERMs to the eNB for EDRs allocation. Next, the number of DRs and the number of DPUs are compared. If the number of DRs is greater than the number of DPUs, the eNB obtains R EDRs for the DPUs and (P-R) DRBs for the NPUs remain in the next DTP. Then, the process moves to a step of allocating resources among the DPUs using a switching scheme according to the degree of competition for channel access.

If the number of DRs is less than the number of DPUs, the eNB obtains all the available DRs for the DPUs at the next DTP (e.g., T = 2). The remaining unscheduled DPUs send the ERMs back to the eNB at the next DTP and then acquire the EDRs at the DTP (e. G., T = 3). DNPUs then compete for DRBs in the DTP by using the MCALOHA / MCALOHA-ES scheme. In addition, changes to _{T = T + 1, DNPU i} _C = DNPU i _C +1.

The switching unit 630 allocates resources among the DPUs using a switching scheme according to the degree of competition for channel access. The switching unit 630 switches the channel access protocol from MCALOHA scheme to MCALOHA-ES to avoid contention if the degree of competition for channel access is equal to or greater than a predetermined threshold.

의 실패 횟수가 미리 정의된 W의 값을 초과하게 되면, 채널 액세스 프로토콜은 경쟁을 피하기 위해 MCALOHA에서 MCALOHA-ES로 스위칭된다. 다시 말해, DNPUs는 MCALOHA 방식에 의해 DRs를 선택한다. 그 결과, 불필요한 재전송 에너지가 감소한다. The switching unit 630 compares the value of the pre-defined W and DNPU _i _C. In the presence of severe competition for channel access, the switching concept is utilized to provide diversity for channel access to DNPUs. In other words, DUE

The channel access protocol is switched from MCALOHA to MCALOHA-ES to avoid contention. In other words, DNPUs select DRs by the MCALOHA method. As a result, unnecessary retransmission energy is reduced.

의 실패 횟수가 미리 정의된 W의 값보다 작은 경우, 해당 DNPUs는 MCALOHA-ES 방식에 의해 DRs를 선택한다. On the other hand, DUE

Is smaller than the predefined value of W, the corresponding DNPUs selects DRs by the MCALOHA-ES scheme.

The search unit 640 performs the D2D search according to the SINR for performing the D2D search. The search unit 640 performs D2D search when the SINR for performing the D2D search is equal to or less than a predetermined threshold value. If the SINR for performing the D2D search is equal to or greater than a predetermined threshold value, the search resource block for DPUs is acquired in the second search cycle.

Next, the value of SINR _i is compared with a predetermined threshold SINR _threshold . If the value of SINR _i is greater than a predetermined threshold SINR _threshold , the UEs can be successfully retrieved.

On the other hand, if the value of SINR _i is smaller than the predetermined threshold SINR _threshold , unsuccessful DNPUs acquire DRs for the next DTP. In addition, changes to _{T = T + 1, DNPU i} _C = DNPU i _C +1.

7 is a diagram illustrating a radio access network shared between NPUs and PS in ProSe LTE according to an embodiment of the present invention.

In the present invention, consider the situation in which DPUs reuse the spectrum with the same CUEs. To avoid such conflicts, PS users in a shared network require specific priorities in resource allocation during critical situations such as disasters and scheduled events such as the Olympics or the World Cup. Referring to FIG. 6, a higher priority is assigned to PS UEs compared to CUEs.

Priority Emergency Services for DPUs in commercial mobile networks should not only limit the amount of connection attempts, but also allow prioritized access to high priority users, including emergency response. There are two main mechanisms for providing high priority to users in terms of resources: one to control resources for accessing the air interface and the other to resources for service-level priorities . In this problem associated with D2D discovery, network priorities are determined based on accesses of the air interface over service-level priorities.

8 is a diagram illustrating a system level simulation environment for performance verification according to an embodiment of the present invention.

Referring to FIG. 8, the performance of the proposed TEECR-DDRA technique is verified in terms of the average number of retrieved users, the range of retrieved UEs, the ratio of successful retrieval of UEs, and the ratio of undetected UEs.

9 is a graph showing the number of users retrieved according to an embodiment of the present invention.

FIG. 9A is a graph showing the CDF of the retrieved users, and FIG. 9B is a graph illustrating the number of retrieved users VS retrieval time.

Figure 9 shows the average number of users searched for search time under the proposed TEECR-DDRA technique. The proposed scheme also considers the QoS requirements and delays of non-PS UEs by enabling enforcement of energy sensing among non-PS UEs when the counter exceeds a certain limit. Therefore, the effect of this increases the maximum number of users retrieved by applying energy sensing to non-PS UEs to 430 as shown in Figure 9 (a). 9 (b), it can be seen that approximately 26 more users are retrieved by using the proposed TEECR-DDRA technique than the RA technique of the prior art.

10 is a graph showing search distances of users according to an embodiment of the present invention.

The TEECR-DDRA scheme proposed in FIG. 10 is superior to the RA of the prior art by searching D-UEs at a long distance. When the simulation results are compared at 50% of the CDF, the search range of the prior art RA technique reaches the maximum range at 100 m. However, the proposed TEECR-DDRA technique increases the distance to 120 m. In addition, the search range gives priority to PUs and increases to 155m by combined gain by energy sensing for NPUs. Therefore, by using the TEECR-DDRA technique, the search range of all users participating in the search is increased compared to the prior art RA technique.

FIG. 11 is a graph illustrating a search coverage success rate of users according to an embodiment of the present invention.

에서 종래기술 RA에 대한 DSR 기법은 대략 36%이고, 반면에 PS 우선 순위 및 에너지 센싱을 갖는 제안된 TEECR-DDRA 기법은 각각 38% 및 40%까지 증가한다. 다른 SINR 디코딩 포인트들에 대한 시뮬레이션 결과는, 종래기술 RA 기법 및 제안된 TEECR-DDRA 기법에 대한 DSR은 각각 0.3% 및 1.9%에 도달한다.
The simulation results in FIG. 11 are graphs for a range of SINR decoding thresholds, ranging from -15 to 15 dB. From the results

, The DSR scheme for the prior art RA is approximately 36%, while the proposed TEECR-DDRA scheme with PS priority and energy sensing increases by 38% and 40%, respectively. Simulation results for different SINR decoding points show that the DSR for the prior art RA scheme and the proposed TEECR-DDRA scheme reaches 0.3% and 1.9%, respectively.

12 is a graph showing a search range failure rate of a user according to an embodiment of the present invention.

It can be seen that the TEECR-DDRA scheme proposed from FIG. 12 always has a lower search failure rate when compared to the prior art. Simulation results are compared at various SINR detection thresholds, and the proposed TEECR-DDRA technique is reduced by 7% in DFR compared to the prior art RA technique. The proposed TEECR-DDRA scheme reduces the DFR because it considers the priority of PS users and channel states of users during DR allocation among users.

The apparatus described above may be implemented as a hardware component, a software component, and / or a combination of hardware components and software components. For example, the apparatus and components described in the embodiments may be implemented within a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable array (FPA), a PLU a programmable logic unit, a microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. The processing device may also access, store, manipulate, process, and generate data in response to execution of the software. For ease of understanding, the processing apparatus may be described as being used singly, but those skilled in the art will recognize that the processing apparatus may have a plurality of processing elements and / As shown in FIG. For example, the processing unit may comprise a plurality of processors or one processor and one controller. Other processing configurations are also possible, such as a parallel processor.

The software may include a computer program, code, instructions, or a combination of one or more of the foregoing, and may be configured to configure the processing device to operate as desired or to process it collectively or collectively Device can be commanded. The software and / or data may be in the form of any type of machine, component, physical device, virtual equipment, computer storage media, or device , Or may be permanently or temporarily embodied in a transmitted signal wave. The software may be distributed over a networked computer system and stored or executed in a distributed manner. The software and data may be stored on one or more computer readable recording media.

The method according to an embodiment may be implemented in the form of a program command 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 to be recorded on the medium may be those specially designed and configured for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI &gt; or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and the claims and their equivalents, are also within the scope of the following claims.

Claims (12)

In a public safety user priority based D2D search method,
Placing DPUs and DNPUs in a network coverage area and initializing parameters;
Allocating search resource blocks for the DPUs and the DNPUs based on a public safety user priority and dynamically adjusting according to the number of DPUs; And
Allocating resources among the DPUs using a switching scheme according to degree of competition for channel access
A public safety user priority based D2D search method. The method according to claim 1,
Wherein the step of allocating search resource blocks for the DPUs and the DNPUs based on the public safety user priority and dynamically adjusting according to the number of DPUs comprises:
If the number of search resource blocks is larger than the number of search resource blocks by comparing the number of search resource blocks with the number of DPUs, the search resource block for the DPUs is acquired in a first search period
Public safety user priority based D2D detection method. The method according to claim 1,
Performing the D2D search according to an SINR for performing the D2D search
Further comprising:
The step of performing the D2D search according to an SINR for performing the D2D search includes:
Performing the D2D search if the SINR for performing the D2D search is less than or equal to a predetermined threshold value,
If the SINR for performing the D2D search is equal to or greater than a predetermined threshold, the search resource block for the DPUs is acquired in the second search cycle
Public safety user priority based D2D detection method. The method according to claim 1,
Wherein the step of allocating search resource blocks for the DPUs and the DNPUs based on the public safety user priority and dynamically adjusting according to the number of DPUs comprises:
Comparing the number of search resource blocks with the number of DPUs to obtain all available search resource blocks for the DPUs in a first search period if the number of search resource blocks is less and the remaining unscheduled DPUs transmits an emergency connection request to the eNB, and secures the search resource block for the DPUs in a second search cycle
Public safety user priority based D2D detection method. 5. The method of claim 4,
The DPUs may compete for securing the search resource block using the MCALOHA scheme or the MCALOHA-ES scheme in a second search cycle
Public safety user priority based D2D detection method. The method according to claim 1,
Wherein the allocating resources among the DPUs using a switching scheme according to the degree of competition for the channel access comprises:
When the degree of competition for the channel access is equal to or greater than a predetermined threshold, the channel access protocol is switched from the MCALOHA scheme to the MCALOHA-ES scheme
Public safety user priority based D2D detection method. A public safety user priority based D2D search apparatus comprising:
An initialization unit for placing DPUs and DNPUs in a network coverage area and initializing parameters;
A search resource block allocator based on a public safety user priority and dynamically adjusting according to the number of DPUs and allocating search resource blocks for the DPUs and the DNPUs; And
A switching unit for allocating resources among the DPUs using a switching scheme according to the degree of competition for channel access;
A public safety user priority based D2D search device. The method according to claim 6,
Wherein the search resource block allocation unit allocates,
If the number of search resource blocks is larger than the number of search resource blocks by comparing the number of search resource blocks with the number of DPUs, the search resource block for the DPUs is acquired in a first search period
Public safety user priority based D2D search appliance. The method according to claim 6,
A search unit for performing the D2D search according to an SINR for performing the D2D search,
Further comprising:
The search unit may search,
Performing the D2D search if the SINR for performing the D2D search is less than or equal to a predetermined threshold value,
If the SINR for performing the D2D search is equal to or greater than a predetermined threshold value, acquiring the search resource block for the DPUs in a second search cycle
Public safety user priority based D2D search appliance. The method according to claim 6,
Wherein the search resource block allocation unit allocates,
Comparing the number of search resource blocks with the number of DPUs to obtain all available search resource blocks for the DPUs in a first search period if the number of search resource blocks is smaller, transmits an emergency connection request to the eNB, and secures the search resource block for the DPUs in a second search cycle
Public safety user priority based D2D search appliance. 11. The method of claim 10,
The DPUs may compete for securing the search resource block using the MCALOHA scheme or the MCALOHA-ES scheme in a second search cycle
Public safety user priority based D2D search appliance. The method according to claim 6,
The switching unit includes:
When the degree of competition for the channel access is greater than or equal to a predetermined threshold, the channel access protocol switches from MCALOHA scheme to MCALOHA-ES to avoid contention
Public safety user priority based D2D search appliance.

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