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What’s the realistic capacity of a 3G HSPA, HSPA+ or LTE network?

Photograph of Mark HeathWe have derived realistic figures for total network capacity per month and network capacity per month per 3G device for a number of operator circumstances, as shown in the table below.

For each technology, the table shows the capacity figures that could be achieved by a typical network implementation if ALL 3G devices supported that technology. In practice, it takes a period of time for new handset technologies to be adopted by the customer base and therefore there it is likely that the 3G devices would have a mixture of capabilities. Hence, these figures can be regarded as the upper bound for the capacity that could be achieved.

Table comparing the network capacity of W-CDMA, HSPA, HSPA+, LTE and LTE-Advanced for different types of network operator

Total network capacity and network capacity per device that can be supported with W-CDMA, HSPA, HSPA+, LTE and LTE Advanced

The calculation of realistic network capacity, shown in the figure below, is relatively complex, and our calculation has taken account of the following factors:

  • that traffic volumes fluctuate at different times of the day. We have calculated network capacity for the busiest period of the day (termed the ‘busy hour’) when the load on a base station is at its highest, and derived the total monthly capacity based on the relationship between busy hour traffic and average monthly traffic seen in practical networks
  • that traffic is not distributed uniformly geographically, so all sectors in a network are not loaded equally. As a result, some base station sectors will be underutilised. Our network capacity calculation includes an element of underutilisation seen in practical 3G networks
  • that some base stations are deployed to provide coverage enhancement, and may not be heavily used (so full inclusion of them in the network capacity calculation would overestimate network capacity). Our network capacity calculation assumes that a proportion of base station sectors do not noticeably contribute towards total network capacity.
Diagram showing the steps in calculating mobile network capacity

Calculation of realistic monthly network capacity and network capacity per device for W-CDMA, HSPA, HSPA+, LTE and LTE-Advanced

To demonstrate how 3G network capacity per device is dependent upon the amount of spectrum, the number of base station sectors and the number of 3G devices, we have modelled a range of 3G operator circumstances:

  • an incumbent 3G operator, with 20 million 3G devices, 15 000 base station sectors and 10MHz of spectrum
  • a new-entrant 3G operator, with only 5 million 3G devices, 15 000 base station sectors and 15MHz of spectrum
  • an incumbent 3G operator, with 20 million 3G devices and 15 000 base station sectors that has acquired additional 3G spectrum (to have 20MHz in total)
  • an incumbent 3G operator, with 20 million 3G devices that has expanded its network significantly (to 25 000 base station sectors) and acquired substantial additional spectrum (to have 40MHz in total).

HSPA networks would be able to support monthly traffic levels per 3G device (if all of the devices could support HSPA) of between 90MB and 602MB, depending on 3G operator circumstances, as shown in the figure below.

Bar chart of HSPA capacities for different types of mobile network operator

Calculated HSPA network capacities for incumbent and new-entrant mobile operators

Compared with fixed broadband networks, which in general can comfortably support high usage levels (say 10GB or more per customer per month), HSPA networks have significant capacity limitations, particularly for 3G operators with modest spectrum allocations and large customer bases. As will be discussed later, 3G operators (particularly incumbents) must be cautious embarking on a strategy to compete aggressively with fixed broadband services.

Incumbent 3G operators with modest 3G spectrum allocations and large customer bases will suffer from the lowest capacity per user. For example, an incumbent 3G operator with a total of 20 million devices and a 3G spectrum allocation of 10MHz would only be able to support average monthly traffic volumes of 90MB per 3G device with HSPA, even if all 3G customers had HSPA devices. In contrast, a new-entrant 3G operator with 5 million 3G devices and 15MHz of 3G spectrum could support more than 0.5GB per device per month with HSPA.

Average monthly usage of several gigabytes is common on fixed broadband networks but would be very difficult for incumbent 3G operators to support with their 3G networks. For example, as shown in the table above, for an incumbent operator with 20 million 3G devices to support monthly traffic of about 2GB per device, it would need to:

  • deploy LTE on a widespread basis
  • significantly increase the number of base stations (adding 10 000 base station sectors)
  • acquire, and utilise, 40MHz of 3G spectrum (which is four times greater than typical allocations currently).
  • ensure that all of its customers (or at least the heavy users) migrate to LTE devices.

Despite extensive hype about the widespread displacement of fixed broadband services by mobile broadband services, there will continue to be a gulf between the ‘last mile’ capacities of fixed and cellular networks, even when LTE is widely deployed. However, in the early stages of LTE deployment, when LTE networks are underutilised, operators will have greater flexibility to compete with fixed broadband services.

Dr Mark Heath co-founded Unwired Insight in 2001, to provide analysis and market intelligence for the mobile telecommunications industry. Previously he contributed to the standardisation of GSM, UMTS and DECT and held senior roles for a mobile network operator and equipment manufacturer. Mark has written over 40 industry reports and has advised investors, network operators, equipment vendors, lawyers and government bodies.

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