Millimeter-wave or 60 GHz communication is a promising technology that enables data rates in multigigabits. However, its tremendous propagation loss and signal blockage may severely affect the network throughput. In current data-centric device-to-device (D2D) communication networks, the devices with intended data communications usually lay in close proximity, unlike the case in voice-centric networks. So the network can be visualized as a naturally formed groups of devices. In this paper, we jointly consider resource scheduling and relay selection to improve network capacity in 60 GHz based D2D networks. Two types of transmission scenarios are considered in wireless personal area networks (WPANs), intra and intergroup. A distributed receiver based relay selection scheme is proposed for intragroup transmission, while a distance based relay selection scheme is proposed for intergroup transmission. The outage analysis of our proposed relay selection scheme is provided along with the numerical results. We then propose a concurrent transmission scheduling algorithm based on vertex coloring technique. The proposed scheduling algorithm employs time and space division in mmWave WPANs. Using vertex multicoloring, we allow transmitter-receiver (
The demand for high-bandwidth applications in the recent years has been growing exponentially. The high-speed Internet has raised users expectations to a level, where they are impatient to wait for their data communication requests. 60 GHz communication network promises data rate in gigabits and can be used in both indoor [
One of the unique characteristics of 60 GHz networks is its tremendous propagation loss which severely affects the data rates. However, unlike traditional networks [
The use of relays in 60 GHz based D2D networks provides an alternative for signal blockage. Relays not only help in signal blockage but also reduce the tremendous propagation loss [
In short-ranged data-centric communication network, the premise that two parties initiate communication to be in close proximity is acceptable contrary to voice-centric networks. Rather, it would be common to have a situation where several co-located devices (DEVs) would like to share contents such as digital pictures or interact for applications such as video gaming and social networking [
The main contributions of this paper include the following.
The rest of the paper is organized as follows. Section
Relay selection and scheduling algorithm for 60 GHz have generated sizable literature [
Apart from relay selection, scheduling algorithms are also proposed for capacity enhancement in conjunction with/without relay selection. More recently in 60 GHz networks, concurrent transmission is encouraged due to its highly directional nature. The concept of concurrent transmission is not new, but coupled with the directional antenna and short-range nature of 60 GHz networks, its effectiveness can be multifolded. The case of concurrent transmission scheduling has been investigated extensively in the literature [
A network based on 802.15.3c with dense deployment of DEVs is considered with one central DEV called PNC. Initially, DEVs are distributed randomly with a PNC in the center with quasi-omni transmission. Over time, due to the tendency of
System model for typical D2D WPAN.
Devices in 802.15.3c suffer from high path loss at 60 GHz frequency band. Therefore, they should focus radiant energy for the data transmissions in the intended direction. Similarly, they may concentrate on the energy for data receptions at a specific direction to gather more power, making it necessary to employ directional communication technologies at the 60 GHz frequency band. The PNC in 802.15.3c should broadcast beacons in all directions since every device connected with the PNC should receive the beacons for proper operations. Quasi-omni is a directional transmission, but it mimics omnidirectional transmission by consecutively rotating its transmission direction through
Highly directional antenna is considered for our model. Directional antennas fall in two categories [
Every DEV employs an antenna with
The capacity of an additive white Gaussian noise (AWGN) channel with broadband interference assumed as Gaussian distribution is given by
We are considering a typical indoor environment with possibility of concurrent transmissions as shown in Figure
As we can see in Figures
Intergroup multihop scenario.
Intragroup multihop scenario.
Assume that relay
In this section, we are focusing on relay selection and scheduling mechanism to enhance D2D networks based on 60 GHz to successfully achieve the data rates it promises.
We first define the relay selection problem as follows. Let
As mentioned earlier, two types of transmissions are considered, inter- and intragroup. It is observed that in high-speed short-ranged WPANs,
In this subsection, we propose a relay selection algorithm for intergroup multihop transmission in mmWave WPANs. Midmost relay positioning, distance, and traffic load are considered to take the relay decision, as mentioned in Algorithm
(1) (2) (3) With (4) (5) say (6) (7) (8) (9) Select (10)
In this subsection, we propose a receiver based distributed relay selection for intragroup transmission. We are considering an antenna with
Table maintained by
Beams | SNR levels | Potential relay DEVs |
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The first column in Table
(1) (2) (3) With active reception of signal at sector (4) (5) Search table for (6) Calculate (7) (8) (9) (10) (11) (12) (13) (14)
Relay to
Relay selection example.
For
In this section, we propose an algorithm for concurrent transmission in 60 GHz based D2D networks employing the principle of vertex coloring (VC). Our proposed vertex multicoloring concurrent transmission (VMCCT) algorithm schedules
In this subsection, we discuss the conditions for concurrent transmission. Figure
Concurrent transmission scenario.
Concurrent flows with mutual interference can be allowed as long as they are apart by a certain threshold distance. The threshold distance is defined as an area where the mutual interference can be seen as background noise. To accomplish this, an exclusive region (ER) around the receiver is defined in [
Both concurrent transmission conditions 1 and 2 realize the possibility of concurrent transmission for different flows. For illustration, as in Figure
A conflict matrix (CM) represents the relationship between different flows. The relationship is represented by 1 (conflict) and 0 (no conflict) as shown below:
Equation (
Conflict graph representation of VC and VMCCT.
Time slot, being scarce resource, requires efficient allocation. We employ VC algorithm to effectively resolve conflict among flows and efficiently assign time resource. VC algorithm has been used for resource allocation in different types of networks [
The conservative time-slot allocation based on VC is not efficient. Our proposed multicoloring algorithm allocates time slots more aggressively to improve network throughput. Algorithm
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28)
The proposed algorithm can be explained with the help of Figure
With (
In Figure
In order to evaluate our proposed relay selection schemes and scheduling algorithm, we consider
Simulation parameters.
Parameters | Values |
---|---|
System bandwidth |
1800 MHz |
Transmission power |
0.1 mW |
Background noise |
−134 dBm/MHz |
Path loss exponent |
|
Reference distance |
1.5 m |
Path loss at |
71.5 dB |
Slot time |
18 |
Number of slots in superframe |
|
We compare our proposed VMCCT scheme [
Figures
Improved average flows throughput versus flow density.
Improved average flow throughput versus increasing beamwidth.
Figures
Improved network throughput versus flow density.
Network throughput versus increasing beamwidth.
In this section, we will evaluate our proposed relay selection schemes. We also have evaluated our proposed VMCCT scheme in multihop scenario using the proposed relay selection schemes. We are considering a typical WPANs scenario, where most of the transmissions are within intragroup with occasional intergroup transmissions. We first evaluate our relay selection schemes and then provide simulation results to show their effectiveness in conjunction with our proposed VMCCT scheme.
In order to evaluate our proposed relay selection schemes, we use outage probability (OP) as metric. OP is an important performance indicator in wireless systems. OP can be defined as the probability that the end-to-end SNR falls below a predefined threshold
Since we are considering two-hop scenario, according to (
For
Hence, OP at a given DEV position can be obtained by inserting (
In this subsection, numerical results are employed to evaluate our proposed relay selection and VMCCT schemes. Ergodic capacity and OP are compared for direct transmission, fixed relay, and our proposed relay selection schemes. The simulation parameters are shown in Table
Outage probability with varying relay distance.
Outage probability with varying
Ergodic capacity with varying
We used our proposed VMCCT algorithm in multihop scenario. Our proposed algorithms try to find a suitable relay placed at near-equal distance from
Average flow throughput in multihop scenario.
Network throughput in multihop scenario.
In order to improve the network capacity in 60 GHz based D2D networks, we jointly consider relay selection and scheduling algorithm. Owing to tremendous propagation loss, distance is used as a main metric for relay selection. Apart from distance, a relay with midmost positioning is encouraged for both inter and intragroup transmission scenarios. A novel distributed relay selection algorithm is proposed for intragroup transmission scenario. The outage probability analysis is provided to compare our relay selection schemes with fixed relay selection schemes. Furthermore, we evaluated our proposed relay selection schemes jointly with scheduling algorithm in single- and multihop scenarios. We have compared our results with GA and TDMA under the same system model. Our proposed scheme outperforms both GA and TDMA in terms of network throughput and average flows per slot. Network throughput and average number of flows per slot are improved by
The authors declare that there is no conflict of interests regarding the publication of this paper.
This paper is supported by the State Key Program of National Natural Science of China (Grant no. 61231009), Beijing Higher Education Young Elite Teacher Project under Grant YETP0429, and National High-tech Research and Development Program of China (no. 2014AA01A701).