AP Coordination in Home Networks
Multiple Access Points Can Improve Home Wi-Fi Coverage: The Secret Sauce is AP Coordination
Before we address AP Co-ordination in Home Networks, it is important to note that average home sizes have been increasing at a steady pace in the past four decades as seen from the figure below.
Increasing Home Size
As consumers, we expect our home Wi-Fi network to be ubiquitous, providing reliable connection speeds wherever we are in the home. A single AP may not be capable of providing whole home coverage, especially in larger sized homes. In a recent blog post, my colleague Vikas Sarawat described how a range of multi-access point architectures have emerged to solve this coverage gap. These architectures solve the whole home coverage problems but there are other gaps that need to be addressed in order to have an overall positive Wi-Fi experience.
Single AP vs. Multiple AP Architecture
For example, most consumer grade access point solutions currently lack a centralized Wireless LAN controller (WLC). In general, a WLC acts as a commander-in-chief which manages and controls all the APs that it serves and thereby leads to network optimization.
In the absence of a centralized WLC, multiple APs do not communicate with each other. In fact, they can at times treat each other as rogue APs that are not even operating on the same network.
Hence, there needs to be some sort of a direct communication protocol between these multiple APs in-order to provide a good Wi-Fi experience to the consumers. Although AP co-ordination has been a topic of research in a controller-based architecture ecosystem (e.g., for enterprise and community Wi-Fi environments) for some years, historically, the residential consumer premise equipment vendors have not paid much attention to coordination since most homes only had a single AP. To address this shortcoming, CableLabs is actively working on defining and standardizing the AP coordination protocols.
Our goal is to have a lightweight AP co-ordination solution that provides the following two benefits:
Optimal AP selection: When there are multiple APs available, many clients rely solely on signal strength to decide which AP to connect to, but it might not always be optimal concerning throughput for the client.
There are often conditions where a lower received signal strength indicator (RSSI) from the gateway AP may provide better throughput than a stronger RSSI from the repeater. The client cannot determine which is the best connection on its own – the infrastructure must inform it. Choosing the best point of attachment in each location is a decision that warrants information and intelligence on the client-side, the network-side, or possibly both.
Client Steering: APs also need to decide when and how to steer clients to the best AP based on network conditions (e.g., load, bands). This is especially important since many clients prefer to stay associated with one Wi-Fi network even though another Wi-Fi network with “better” connectivity is available. This is commonly referred to as the "sticky client" issue.
With AP co-ordination, the APs can exchange information on how best to get rid of the sticky client problem in a standard fashion. A partial solution has been defined in the IEEE 802.11k and 802.11v standard but not many APs or clients implement them yet.
While the IEEE 802.11k defines methods of retrieving information from clients in the form of neighbor requests and reports, the IEEE 802.11v standard provides the AP with the ability to configure client stations wirelessly in the form of the BSS Transition Management (BTM) feature.
To summarize, AP coordination is an important topic of research, particularly within the home networks where there is no WLC. CableLabs is actively engaging with the vendor community to develop a standard way of implementing in-home AP coordination protocols which we plan on submitting to the standards bodies such as WFA and WBA in the near future.
Are Wi-Fi Repeaters and Extenders Beneficial?
Subscribers today often supplement their existing Wi-Fi Access Points (AP) with wireless repeaters and extenders to enhance Wi-Fi coverage within the home network. Frequently, we are asked if these devices provide any real benefit.
To answer these questions, we ran some tests in a house to measure and compare the relative performance of a couple of off-the-shelf wireless repeaters and extenders.
Results from the field tests
Since the industry is all over the place with the definition of Repeaters and Extenders, we came up with our definition. We define a Wi-Fi repeater as a device that uses a single radio and channel to relay traffic between a client and an AP. Since the repeater uses the same channel to relay data between the client and the AP, the data must be on the channel/radio twice. A Wi-Fi extender, on the other hand, is a device with two or more radios that dedicate one radio and channel to bridge client traffic to/from an AP, while using another radio and channel to communicate with clients. For our comparison we used the following configurations.
Figure 1: Repeater and Extender Configuration
A single AP without any repeaters or extenders provided coverage with -67dbm or better RSSI within the test house. As we expected and also demonstrated in Figure 2, the wireless repeaters and extenders did help in extending the wireless coverage. We observed this coverage increase in at least four locations outside the home. Inside the house, we observed a new minimum RSSI of -50 dBm with extenders and -58 dBm with repeaters (17 dB and 11 dB respectively better than with the AP alone). Additionally, our findings also demonstrate improvements in client throughput performance not only in the extended coverage areas but also in some of the areas otherwise covered with the AP.
Figure 2 - Throughput vs. Path Loss:
Baseline AP vs. (AP + Repeater) vs. (AP Extender)
In our testing, the extender provided better coverage improvements and throughput than the repeater. The better coverage improvements with the extender are due to the fact that the extender is using a 2.4 GHz band for the fronthaul, while Wi-Fi repeater is using the 5 GHz band. The 2.4Ghz supports better propagation characteristics compared to the 5Ghz band. The extender configuration offered better throughput performance in the extended areas than the repeater. Primarily, this is because the repeater time-shares the same channel to communicate to the client (front-haul) and AP (backhaul). The extender, on the other hand, uses a separate radio and channel to communicate to the client (front-haul) and AP (backhaul).
Are there any unexpected surprises to be aware of with multiple Wi-Fi nodes in a home?
A significant observation from the test results is that the client did not always connect to the Wi-Fi node with the “best” throughput performance. In some locations (represented with green dots in Figure 3), the client chose to connect to the repeater, even though it would have got a better throughput had it connected to the AP. The client appeared to be making Wi-Fi node selection decisions solely based on the received signal strength, which may result in sub-optimal or even very poor network performance. Since a client has limited avenues for knowing which node will offer better throughput, this warrants the need for coordination between the APs, and also between the AP and client in the home.
CableLabs is actively working with the Wi-Fi Alliance (WFA) to develop new certifications (e.g., MBO) programs to enable coordination between AP and clients. We are also engaging with the CPE vendors about the need for AP coordination.
Figure 3: Throughput vs. Path Loss: AP versus AP + Repeater
As shown in this blog, the Wi-Fi repeater and extenders are helpful in extending Wi-Fi coverage. However, some coordination between AP and repeater/extender devices is needed to make sure clients are always connected to the “right” node.
Vikas Sarawat is a Director in the Wireless (R&D) Group at CableLabs.