The IEEE 802.11ad technology, which allows wireless devices to communicate in the unlicensed 60 GHz ISM band, promisingly provides multi-Gbps data rates for bandwidth-intensive applications. After years of research and development, we are now observing an increasing number of commodity IEEE 802.11ad radios that motivate researchers to exploit the IEEE 801.11ad capability for applications. This work first conducts an empirical study on the IEEE 802.11ad performance. In particular, we characterize the performance of IEEE 802.11ad links considering the variation of network parameters and interference. Secondly, we investigate the possibility of introducing IEEE 802.11ad to an evolving Wi-Fi network. The evaluation results show that our off-the-shelf IEEE 802.11ad hardware can achieve the Gbps level throughput of the transmission control protocol (TCP) and user datagram protocol (UDP). However, the evolvement is not trivial since the hardware can not well maintain the 60 GHz link. The main reason is lacking the fast switchover function between an IEEE 802.11ad and a legacy Wi-Fi link. We then seek the potential of multipath TCP (MPTCP) for the expected switchover. The default MPTCP, which enables data transmissions on both the IEEE 802.11ad and Wi-Fi links, is harmful to the IEEE 802.11ad throughput. Meanwhile, the backup mode of MPTCP, in which the Wi-Fi link acts as a backup for IEEE 802.11ad one, can maintain the comparable performance. Therefore, we propose to adopt MPTCP with the backup mode in the evolving Wi-Fi networks. The efficiency of MPTCP-based switchover is confirmed by conducting real experiments.
In recent years, the popularity of wireless devices and the explosion of wireless traffic require ever-increasing demands on better network performance [
The IEEE 802.11ad physical layer uses 2.16 GHz-width channels that theoretically provide data rate up to 6.76 Gbps per single channel. Moreover, the IEEE 802.11ad radio with directional beams can improve the spatial use. The IEEE 802.11ad signal, however, incurs much higher attenuation than the one of legacy Wi-Fi. To compensate for the path loss, the IEEE 802.11ad device uses high gain antenna arrays, which on the other hand introduces a new challenge of link maintenance (e.g., when blockage exists). The maintenance is expected to be realized by switching to a legacy Wi-Fi link when the IEEE 802.11ad link is not available. Accordingly, numerous efforts in research and development have led to the advent of low-cost, low power, off-the-shelf IEEE 802.11ad devices [
This work first addresses the issue of performance characterization; we empirically evaluate an off-the-shelf IEEE 802.11ad hardware in a typical office environment towards the achieved multi-Gbps throughput. The performance metrics of IEEE 802.11ad links have been extensively investigated under the variation of different network parameters and interference. In particular, we consider the existence and nonexistence of two typical types of IEEE 802.11 interferences (i.e., cochannel and adjacent channel). Moreover, we also scrutinize the network parameters such as signal strength, modulation and coding scheme (MCS), Maximum Transmission Unit (MTU), and traffic types (i.e., TCP and UDP). Thanks to the support of the IEEE 802.11ad driver and associated tools, we can find the multi-Gbps throughput (for both TCP, UDP) following the conditions of modulation and coding scheme (MCS) set, signal strength, and MTU. We also quantify the traditional interference effects on the throughput and lost packet metrics.
Secondly, targeting the evolvability issue, thoroughly investigate the capacity of link maintenance (i.e., the most significant challenge of 60 GHz communication). Our evaluation shows that the IEEE 802.11ad link itself can neither bypass the blockage nor handle the change of antenna direction. That is because there is a lack of the function of fast switchover between the IEEE 802.11ad and a legacy Wi-Fi link. We then seek the possibility of multipath TCP (MPTCP), which is capable of exploiting multiple wireless links concurrently, for the switchover. Our investigation points out that the default MPTCP (i.e., full mesh mode) that simultaneously uses the IEEE 802.11ad and Wi-Fi links for data transmission is not efficient. The overall throughput is largely varied and is always smaller than the TCP throughput of IEEE 802.11ad link. On the other hand, the backup mode of MPTCP, in which the IEEE 802.11ad and Wi-Fi links are in an active/standby state, guarantees the comparable throughput. Therefore, we propose to adopt MPTCP with the backup mode for the switchover. The efficiency of MPTCP-based switchover has been confirmed by conducting the real experiments.
The remainder of this paper can be outlined as follows. The following section presents related works. In Section
The experimental study is a popular method for understanding the performance characterization in IEEE 802.11 (Wi-Fi) networks. The method has shown its usability with different IEEE 802.11 versions such as IEEE 802.11n [
On the other hand, the off-the-shelf IEEE 802.11ad hardware is gaining popularity after years of efforts in R & D. That attracts the experimental studies on the IEEE 802.11ad performance. The most related one to ours is [
The link maintenance capability, which is critical for the evolvement of IEEE 802.11ad, has been investigated in several related works. In [
In this section, we first describe the overview of IEEE 802.11ad. After that, we present the experiment environment and the measurement results.
The IEEE 802.11ad standard supports peer-to-peer and infrastructure connections. In an IEEE 802.11ad link, each end’s physical layer executes a beamforming mechanism to form directional transmit/receive beams using a phased-array antenna. There are four types of PHY layers in the standard (i.e., control PHY, OFDM PHY, Single Carrier (SC) PHY, and Low Power SC PHY), each of which supports a set of MCSs. In the 2012 version, the channel list for IEEE 802.11ad operation in the 57-63 GHz band includes four channels as presented in Table
IEEE 802.11ad channel list.
Channel | Center | Minimum | Maximum | Bandwidth |
---|---|---|---|---|
(GHz) | (GHz) | (GHz) | (GHz) | |
1 | 58.32 | 57.24 | 59.4 | 2.16 |
2 | 60.48 | 59.4 | 61.56 | 2.16 |
3 | 62.64 | 61.56 | 63.72 | 2.16 |
4 | 64.8 | 63.72 | 65.88 | 2.16 |
The 60 GHz link has a problem with blockage vulnerability. Moreover, the antenna direction may change in operation. Therefore, the link maintenance is vital to efficiently evolve IEEE 802.11ad on Wi-Fi networks. For that purpose, the IEEE 802.11ad standard defines the Fast Session Transfer (FST) protocol [
We conduct our investigation using a testbed deployed in a typical office environment. Each IEEE 802.11ad link is constructed by a pair of radio modules, which are produced by Panasonic Inc., Japan. Each module is connected to an Ubuntu 14.04 LTS machine that includes the supporting drivers and monitoring utilities. The radio module can run in the client or personal basic service set (PBSS) control point (PCP)/access point (AP) modes. The IEEE 802.11ad defines antenna beams as narrow as 2.86-degree. However, the investigated IEEE 802.11ad module uses 50-degree beam width [
Supported single carrier PHY modulation and coding scheme.
MCS | Modulation | Repetitions | Coding | Rate |
---|---|---|---|---|
Index | Rate | (Mbps) | ||
1 | | 2 | 1/2 | 385.0 |
2 | | 1 | 1/2 | 770.0 |
3 | | 1 | 5/8 | 962.5 |
4 | | 1 | 3/4 | 1155.0 |
5 | | 1 | 13/16 | 1251.0 |
6 | | 1 | 1/2 | 1540.0 |
7 | | 1 | 5/8 | 1925.0 |
8 | | 1 | 3/4 | 2310.0 |
9 | | 1 | 13/16 | 2502.0 |
The investigation begins with checking the signal quality of IEEE 802.11ad link (i.e., ranges of RSSI values) in our environment. To identify the range of RSSI, we record the RSSI values every 0.1 seconds while varying the distance and direction between the pair of IEEE 802.11ad radios. We found that the IEEE 801.11ad link can communicate within the signal range of (-41 dBm, -69 dBm). In the following experiments, we define the strong signal scenario where the RSSI value is kept within (-41 dBm, -43 dBm) and the RSSI value in the weak one is within (-65 dBm, -69 dBm).
We then investigate the TCP and UDP throughput of IEEE 802.11ad link under the combination of all supported MCSs and the link quality scenarios. We also consider different sizes of MTU since they largely affect the throughput. For the high throughput purpose, the link should use the maximum supported MTU. Besides, there are cases of communicates to a far destination (e.g., more than one hop or accessing the Internet). In such cases, the communication is likely limited by a common MTU on the end-to-end path. Therefore, we select the value of 1500-byte MTU, which is typical on Wi-Fi networks and the Internet. We then evaluate the maximum supported MTU (7912 bytes) to observe the full capability provided by the hardware. The evaluation results expose distinct patterns in the behavior of throughput concerning different traffic types, MCSs, and MTUs. We provide a representative subset of our results that show the patterns as mentioned earlier in Figures
Throughput in strong signal and 1500-byte MTU scenario.
Throughput in weak signal and 1500-byte MTU scenario.
Throughput in strong signal and 7912-byte MTU scenario.
Throughput in weak signal and 7912-byte MTU scenario.
The measured throughput of UDP and TCP traffic with 1500-byte MTU in the different signal scenarios are shown in Figures
However, we have a different observation in the case of 7912-byte MTU as shown in Figures
From the above observations, we can conclude that the multi-Gbps throughput of IEEE 802.11ad link has been achievable with both the TCP and UDP traffic. However, those high throughput values depend on the signal strength, PHY rates, and MTU on the system.
This section investigates the effects of conventional interference factors (i.e., adjacent channel interference (ACI) and cochannel interference (CCI)) on the IEEE 802.11ad performance. ACI means wireless transmission on a specific channel suffers interference from channel leakage of its adjacent channels. Meanwhile, CCI indicates the effect of two communications that share a channel without being aware due to the known hidden terminal problem. The hidden terminal problem occurs when two transmitters are not in the transmission range of each other but the carrier sensing range. Due to the beamforming, the nearby position of am IEEE 802.11ad transmitter is within the carrier sensing range if it is outside of the directional transmission.
We set up an additional IEEE 802.11ad link with the strong signal as the interferer to evaluate the interference effects. An
Comparison of UDP normalized throughput.
Comparison of lost packets.
In Figure
In Figure
We further investigate ACI and CCI with the same setup of two IEEE 802.11ad links (i.e., strong signal, 7912-byte MTU); the traffic characteristic over the two links is however different. In this case, we try to start the traffic flows on the two links concurrently with both TCP and UDP traffic. In each experiment, when the
Throughput comparison in ACI scenario with concurrent start of two flows.
Throughput comparison in CCI scenario with concurrent start of two flows.
This section first investigates the capability of link maintenance in IEEE 802.11ad. We then present a method of realizing the link maintenance using MPTCP.
The link maintenance is critical in IEEE 802.11ad since the antenna may temporarily change directions or incur blockage. We hence check the ability of link maintenance on our hardware. We set up a traffic flow running over the IEEE 802.11ad link in 60 seconds. During the period, we observe the variation of traffic under two events: temporary introducing blockage and turning antenna directions. The throughput variation is plotted in Figure
Throughput variation with introducing blockage and changing antenna direction.
MPTCP introduces an additional layer between the application layer and the transport layer in the networking stack. MPTCP does not require any modification in the application or lower layers. MPTCP divides the application data into several subflows (i.e., similar to TCP connections), each of which contains data packets following a different path from a sender to a receiver. The received packets at the receiver are restructured based on their data sequence number. The default operation mode of MPTCP (i.e., full mesh) aims to maximize the usage of all available paths for throughput improvements. In the other modes, MPTCP can use a subset of available paths while putting the remaining paths in a standby condition. With the different modes of operation, as well as two levels of sequencing (i.e., subflow and data), MPTCP theoretically supports the automatic switching and shifting traffic between paths.
MPTCP is however designed for the LTE/Wi-Fi environment. Its potentiality and applicability in the evolving Wi-Fi network (i.e., with IEEE 802.11ad) in practice are not yet known. Besides, the legacy Wi-Fi and IEEE 802.11ad link have the significant difference in characteristics, which may cause unexpected harmful behaviors (e.g., bad packet reordering, inflated or false retransmission timeout, link overshoot, etc.) during the switchover. Addressing those, we investigate two possible operational modes of MPTCP (i.e., namely, full mesh and backup) in the evolving Wi-Fi network. In the former mode, the Wi-Fi and IEEE 802.11ad links are concurrently used for transmitting data (i.e., supporting active/active switchover). In the latter, one link is a backup for the other (i.e., active/standby switchover).
We construct an evolving Wi-Fi network that includes IEEE 802.11ad, legacy Wi-Fi link, and MPTCP to investigate the capability of MPTCP. The network is shown in Figure
Evolving Wi-Fi network.
We initially explored the MPTCP’s two modes in normal conditions (without link error) in the network. The performance metric under investigation is inherited from the aggregation benefit function, which has been proposed in the literature [
To identify
Comparison of aggregation benefit.
Throughput comparison between MPTCP in two modes and TCP.
We then explore the effects of MTU size on the throughput performance of MPTCP. We aim to change the MTU value on each wireless link and to repeat the previous
Throughput comparison between the full mesh and backup modes with different MTU sizes.
We further observe the throughput of MPTCP full mesh with all the supported MCSs in comparison to the one of TCP over IEEE 802.11ad link, which is similar to the MPTCP backup throughput. At each PHY rate, we collect and calculate the average, minimum, and maximum values of measured throughput of ten runs. We show the values in Figure
Comparison of TCP/MPTCP backup and MPTCP full mesh.
In the following, we investigate the performance of MPTCP with the backup mode in the context of achieving the switchover in the evolving Wi-Fi network. The backup mode lets the IEEE 802.11n link be in a standby state for MPTCP packets in a normal condition. The IEEE 802.11n link will be active for MPTCP transmission when the IEEE 802.11ad link is not available. In this investigation, we keep the traffic condition similar to the previous one in the MPTCP evaluation. However, we additionally introduce the events of inactive, reactive links as follows. A period after starting the experiment, we change the direction of the IEEE 802.11ad radio on the MB until the IEEE 802.11ad link becomes inactive (i.e., note that this event is considerably similar to inserting blockage). After another period, we turn the radio back to the original direction for reactivating the IEEE 802.11ad link. During the experiment, we track the instantaneous throughput values at every 0.1 seconds; we then show them in Figure
Achieving switchover with MPTCP backup.
With the advent of new off-the-shelf IEEE 802.11ad wireless devices, which can provide Gbps “wire like” experience to Wi-Fi networks, it is necessary to investigate the capacity of IEEE 802.11ad hardware to introduce the multi-Gbps capability to evolving Wi-Fi networks efficiently. This work first provides an in-depth experimental study on IEEE 802.11ad links in a typical office environment under the variation of network and interference conditions. We confirm the multi-Gbps throughput of both the UDP and TCP traffic with the constraints of signal strength, MCSs, and MTUs. Secondly, we verified that the link maintenance problem (e.g., due to blockage or changing antenna directions) still exists. To solve the problem, we propose to use MPTCP as a mean that provides a fast switchover between an IEEE 802.11ad to a legacy Wi-Fi link. Our evaluation results show that the IEEE 802.11ad radios can evolve on an existing Wi-Fi network. In particular, MPTCP with the backup mode could efficiently switch the multi-Gbps traffic on IEEE 802.11ad to a legacy Wi-Fi (i.e., IEEE 802.11n) link and vice versa.
The experimental data used to support the findings of this study are available from the corresponding author upon request.
The preliminary results of this research have been presented in the 2017 IEEE International Conference on Communications Workshops (ICC Workshops) [
The authors declare that they have no conflicts of interest.
This research was conducted under a contract of R&D for Expansion of Radio Wave Resources, organized by the Ministry of Internal Affairs and Communications, Japan. Additionally, the first author is supported by the Leading Initiative for Excellent Young Researchers (LEADER) program from the Ministry of Education, Culture, Sports, Science and Technology, Japan.