Mobile Broadband ­ How Fast? Mobile operators and…

              Mobile Broadband ­ How Fast?
Mobile operators and equipment suppliers sometimes talk about the "peak" download
and upload speeds provided by a Mobile Broadband or HSPA connection. These
peak rates are the maximum capability of the radio connection between the
customer's mobile device (be that a mobile phone, laptop or something else) and the
radio mast that they are communicating with.

However, the actual speed of a mobile broadband connection experienced by a user
can vary significantly depending on a number of factors, explained below. Here are
six of the primary factors that determine how fast a connection performs at any one
time, or affect the end user's perception of that performance:

1. Technology overheads

The content being downloaded or uploaded by users on a mobile network is only one
element of the total traffic that is being transmitted and received at any one time.
Messages are sent to the network to authenticate the user, to control the service
itself and to indicate if the user is moving from one cell to another.

There are also pieces of information that have to be transported about who the end
user is, where the data that is being sent came from and how the data being received
should be handled by the customer's phone or computer.                 Some software
applications have additional signalling requirements that take a further portion of the
available bandwidth. These elements are essential to the operation of the service,
the network and the end user device's correct functioning, but can reduce the
amount of bandwidth available to carry content that is visible to the mobile user.

In addition some devices that have mobility `added on' to their normal functionality via
datacards or dongles, may not be optimised for mobility, which further impacts the
observed performance.

2. Simultaneous connections

Each radio mast in a mobile operator's network can only support a finite amount of
traffic (depending on the radio technology in use) at any one time. This means that
each radio mast can only provide a limited number of mobile users with the peak rate
of bandwidth simultaneously. Since the radio signal is a shared resource, when that
maximum number of subscribers is exceeded, the bandwidth available to all
subscribers declines proportionately.

3. Network coverage

Although mobile broadband coverage is expanding steadily, not every radio mast has
yet been upgraded to support high bandwidth connections and a Mobile Broadband
service may simply not be available in some areas. Where Mobile Broadband
coverage exists, the laws of physics mean that the further a user is from the radio
mast providing the mobile connection, the lower the bandwidth that will be available.

4. The immediate surroundings

Mobile connections are radio waves and can be degraded by other radio waves. If
there is a source of radio interference located near the user and the radio mast, the
speed of the connection may decline. Mobile connections are also impeded by
obstructions, such as tall buildings, hills and bad weather. This is why mobile
connections deep within buildings tend to be weaker than outside connections.

The quality of a Mobile Broadband connection may also be impacted by the speed at
which the user is moving. For example, a fast-moving train may require the mobile
network to repeatedly hand over the connection from one radio mast to another,
reducing the traffic throughput slightly.

5. Unexpected changes in demand

When mobile networks are designed and built, certain assumptions are made about
how many users will be active at any one time, and the type of traffic they are likely to
be generating. For example, the network's designers may assume that 100 users
will be connecting to a radio mast at any one time. However, some of these users
may be making voice calls, sending text messages or using other frugal applications
and they are unlikely to all require the theoretical maximum bandwidth of 3.6
megabits per second, for example, at once. Therefore the radio mast may only be
required to handle 15 megabits per second of traffic at any one time. Based on this
assumption, a connection allowing for 15 megabits per second will be installed
between the radio mast and the operator's core network.

However, if usage patterns rise unexpectedly (an example of this is the growing
popularity of video streaming), then the network designer's assumptions may prove
to be conservative and the connections between the radio mast and the network
become overloaded. This results in the throughput of traffic being reduced. Such
effects are likely to be observed at times of peak usage.

6. The Internet

Many of the services transmitted via a Mobile Broadband connection are based
somewhere in the Internet. The Internet itself is often subject to congestion that
simply results in traffic arriving slowly, so even if the mobile connection is delivering
the maximum possible bandwidth, the content requested by the end user is not
necessarily delivered at that speed.

Fixed networks also vary in performance

Some of these issues affect other broadband technologies. The fixed-line broadband
technology used by many households is called Digital Subscriber Line (DSL) and this
is also affected by factors 1, 5 and 6 to a greater or lesser extent. For example,
conservative traffic assumptions are creating bottlenecks in DSL networks as usage
rises dramatically with the advent of applications that stream video-on-demand, such
as the BBC's iPlayer.

DSL is also impacted by something similar to factor 3, since the distance between
the customers' premises and the telephone exchange determines the amount of
bandwidth available to the customer. However, as this distance is fixed the peak data
rate offered to an individual is usually adjusted to take this factor into account. DSL
is also occasionally affected by factor 5, since the wires that make up the connection
to the home are often not protected against interference.

The other predominant fixed-line broadband technology used by households today is
cable. Again this is affected by factors 1, 5 and 6 above and also suffers from affects
similar to factor 2 since the bandwidth made available to customers is a shared
resource and so, at peak usage times, connection speeds drop due to the resource
having to be shared between a large number of users.