We are often asked the following questions:
- Why is my WiFi connection slower than my ethernet connection?
- What is good performance for my WiFi network?
It's not uncommon to experience slower WiFi speeds compared to wired ethernet connections. We will explore the reasons behind this disparity and discuss the factors that determine good performance for a WiFi network.
Why is my WiFi connection slower than my ethernet connection?
To understand why WiFi connections tend to be slower than ethernet connections, it's essential to grasp the basics of how a WiFi network functions.
WiFi technology utilizes radio waves to transmit signals between devices. Very simply, by transmitting data “through the air,” WiFi is more susceptible to failure. For example, the distance your device is from the nearest access point, the line of sight your device has to an access point, overlapping WiFi channels, dynamics of WiFi protocols, and device limitations all contribute to WiFi performance issues.
There are two primary components crucial for achieving good network speed and coverage in WiFi deployments: capacity planning and Radio Frequency (RF) planning. However, these components become more complex in environments with a high number of users and devices.
Another factor that affects WiFi speed is the fact that it operates on a half-duplex medium, meaning it can't send and receive data simultaneously like ethernet, which is a full-duplex medium.
We go into more detail on why WiFi is slower than a wired connection here.
Understanding WiFi Network Performance
What is the ideal performance (speed) do I need for different types of work?
The required throughput for various applications can vary significantly. Here are some general guidelines for the TCP throughput consumption of common tasks:
Please note that these figures are approximate and can vary depending on factors such as the specific application, the number of users, and other considerations. For more detailed information, refer to table 13.2 of the CWNA guide, one of the best WiFi deployment guides available.
What is Phy Rate?
To evaluate the performance of a WiFi network, it's essential to consider the physical rate (Phy Rate) and the actual device data throughput.
The Phy Rate represents the theoretical maximum speed at which data can be transmitted between a wireless router or access point (AP) and a WiFi client device, such as a smartphone, laptop, or other Wi-Fi-enabled devices. The Phy Rate depends on various factors, including RF channel bandwidth, the number of antennas on the devices and access points, modulation schemes, and the number of simultaneous devices connected to an AP.
However, the actual device data throughput, or the effective speed experienced by users, is typically lower than the maximum Phy Rate due to various factors such as distance, obstructions, interference, network overhead, and network congestion.
Factors Affecting WiFi Network Performance
- Distance: As the distance between the access point and the client device increases, the signal strength decreases, leading to lower data rates.
- Obstructions: Physical objects like walls and furniture can weaken the wireless signal, resulting in reduced data rates.
- Interference: Other wireless devices, such as microwaves or competing Wi-Fi networks, can cause interference and reduce data rates. To mitigate this, deploying 20MHz channels when necessary can help minimize interference.
- Network Overhead: WiFi networks utilize a portion of their bandwidth for management and control functions, reducing the available data throughput for user traffic. The actual throughput represents the payload data, excluding the overhead.
- Netwok Congestion: The more devices connected to a Wi-Fi network, the higher the contention for available bandwidth, which can lead to reduced data rates for individual devices.
Designing a WiFi network to minimize the impact of these factors is essential. However, it's crucial to note that the realistic achievable throughput estimate is typically around one-third (⅓) of the maximum Phy Rate.
What is good performance for my WiFi network?
Meter networks currently run the 802.11ac WiFi standard, also known as WiFi 5. WiFi 5 operates exclusively in the 5 GHz band and can support various channel widths and spatial streams.
Your device’s capabilities have a significant impact on throughput.
A good signal quality indicator can come from its MCS index: a combination of signal strength, noise level, the physical distance between an AP and a device, and line of sight.
The number of antennas in WiFi devices significantly influences their performance and capabilities. Having more antennas can enhance signal reception, extend the range, and reduce interference.
Moreover, advanced WiFi technologies in newer WiFi standards such as MIMO (Multiple Input Multiple Output) and beamforming utilize multiple antennas to facilitate simultaneous data transmission and reception. These technologies also enable targeted signal transmission, resulting in improved overall performance.
The typical number of antennas in common WiFi-enabled devices:
Note: Spatial Streams (SS) are less than or equal to the number of antennas on a client device, such as a laptop or phone.
Max PHY Rate and Realistic Rates for WiFi 5 Clients
For WiFi 5 clients operating under different configurations, here is a table showcasing the maximum PHY data rates and realistic PHY rates based on channel bandwidth and spatial streams:
If the client device is 802.11n (pre WiFi 5) refer to the following table:
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For more precise PHY rates with different settings, refer to MCS Index.
What reduces optimal WiFi performance? WiFi Overheads and Contention
Achieving the maximum PHY rate is challenging due to various overheads and contention present in WiFi networks. Here are some key factors to consider:
- WiFi Overheads: WiFi networks have significant overhead due to factors like TCP/IP and Ethernet overhead, management frames, half-duplex operation, CSMA/CA (Carrier-Sense Multiple Access with Collision Avoidance) mechanism, WiFi packet ACKs, collisions, retransmissions, hidden node problems, and coexistence of different WiFi standards.
- Network Congestion: The shared nature of WiFi spectrum means that the transmission and reception rates are asymmetric. The channel utilization and the number of devices attempting to transmit simultaneously can significantly impact performance.
The topic of WiFi Overheads is inherently complex. To provide further context and detail, we have included additional information in the appendix.
If you still have questions or need any support, feel free to contact the Meter support team support@meter.com.
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Appendix
Understanding WiFi Overheads
In ideal conditions, several factors contribute to optimal WiFi performance:
- Clear line of sight between the access point (AP) and the device.
- Distance between the AP and device ranging from 3 ft to 15 ft. Typically, being outside the dip in the RF antenna pattern occurs at around 3 ft.
- A small number of active clients connected to the AP, usually between 5 to 10 clients sending traffic.
- Good transmission (tx) and reception (rx) antennas on the client device.
- All clients operating above the minimum basic rates, which are typically 12 Mbps or higher.
- No interference on the AP channel.
Under these ideal conditions, the throughput on a single client can be expected to reach approximately 65% to 70% of the PHY (physical) rate, with a potential peak of up to 80% of the PHY rate. However, in real-life situations, factors such as overhead and contention can cause the throughput to fall between 33% to 50% of the client's PHY rate.
WiFi overhead is relatively substantial, which explains why we don't typically observe a PHY speed of 400 Mbps on a client with specifications like 2x2, 256 QAM, ⅚ coding, and short GI (MCS index of 9). In practice, the maximum achievable throughput is around 400 x 70% = 280 Mbps.
Overhead and Contention
TCP/IP and Ethernet Overhead:
- On wired Ethernet, there is approximately 5% overhead due to TCP/IP and Ethernet frames, resulting in a throughput of 95% of the physical (PHY) rate.
- This overhead is similar on WiFi, excluding retransmissions.
Management frames:
- Management frames, such as 802.11 beacon frames, need to be transmitted at the slowest modulation to ensure all wireless devices on a given channel can receive and decode them. This means, devices that are furthest from the AP (which are already running at slowest speeds) can successfully receive and decode these frames.
- For example, beacon frames are sent at 1 Mbps on the 2.4GHz band and 6 Mbps on the 5GHz band.
- More SSIDs on an access point (AP) cause increased management frame overhead.
- The overhead can range from 3% to very high, depending on the specific circumstances. See this article for more details.
Half Duplex:
- Unlike Ethernet, WiFi does not have separate spectrums for download and upload.
- Both download and upload traffic share a common channel, meaning that when a client is downloading, it is also transmitting acknowledgement (ACK) packets simultaneously.
- This overhead can range from 2% to 4% relative to the client's activity.
- For example, when a client is downloading a file at 150 Mbps, it is also uploading at 2 Mbps at the same time.
Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA):
- Because WiFi is a shared spectrum, devices (clients and access points) need to know when it is safe to transmit on a given channel. WiFi devices use Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) to determine when it is safe to transmit on a given channel.
- To ensure fair access to the channel, devices waiting to transmit must wait for a random amount of time, dependent on channel utilization.
- This overhead can significantly increase if there are many devices attempting to transmit simultaneously. CSMA/CA works really well when there are not many devices wanting to transmit at the same time, which is how WiFi typically works. But this overhead can increase dramatically if there are too many devices trying to transmit at the same time and each client’s “random wait period” keeps adding up.
WiFi Packet ACKs:
- Every WiFi packet sent must be acknowledged (ACK) to confirm receipt.
- A small timing window is appended to each packet, allowing the receiver time to transmit the ACK.
Collisions and Retransmissions:
- High channel utilization and collisions lead to packet loss and subsequent retransmissions when multiple devices want to transmit at the same time on a given channel.
- Co-Channel, overlapping channel, and Adjacent channel interference in dense environments can also contribute to collisions.
Hidden Node Problem:
- In situations where two clients can hear the access point (AP) but not each other, simultaneous transmissions from both clients cause collisions on the AP's side, resulting in the loss of both transmissions.
Coexistence of 802.11n and 802.11ac, and wide channels:
- When a wide channel and a 20MHz client operate on the same channel, there is an overhead in the form of a "request to send" (RTS) and "clear to send" (CTS) before each message, slowing down overall transmission.
It's important to remember that WiFi is a shared resource, and the transmission and reception rates are asymmetric based on various factors. In scenarios where different clients have different PHY rates, the channel usage is divided between them proportionally.