Universal Mobile Telecommunication System (UMTS)
HSUPA

The HSUPA is firstly introduced in UMTS Release 6 and it increases maximum uplink bit rates up to 5.76 Mbps per cell. While HSDPA brings software modifications only to the NodeB and the RNC, HSUPA modifies also the UE. This is quite logical since the purpose of HSUPA is to increase capacity in uplink and thus some changes have to be applied to the UE as well. The principle of HSUPA is similar to HSDPA as it moves fast scheduling and fast data retransmissions to NodeB as indicated in Figure 21. While the principle of fast data retransmissions is analogical to HSDPA with implementation of HARQ, the fast scheduling approach is quite different (as explained bellow). In addition, in HSUPA there is no fast link adaptation to changing channel conditions as in case of HSDPA. Nevertheless, variation of channel is handled by fast power control.

The HSUPA enhancements to NodeB – Comparison with Release 99 and Release 4

## Fast data scheduling

The most notable difference between HSDPA and HSUPA data scheduling is that in downlink (HSDPA), radio resources are shared between individual users whilst in uplink (HSUPA), all active users have assigned certain amount of resources simultaneously. Depending on UE capabilities, scheduling is done either every 10 ms (mandatory) or 2 ms (optional).

The principle of fast data scheduling in HSUPA is as follows. Whenever the UE has data to be transmitted, first, it needs to send request for radio resources allocation in uplink. After that, the NodeB assigns radio resources to the UE. Data scheduling in HSUPA is performed by means of enhanced management of UE’s transmission power.

Since WCDMA is adopted in UMTS, the system is mainly limited by maximal transmitting power and consequently by the interference. To that end, by radio resources is meant rather the amount of transmitting power that could be utilized by individual UEs than the amount of bandwidth (the maximal allowed received power by the NodeB is defined by the RNC). Consequently, the allocation of radio resources by means of fast data scheduling is done in a sense that the UE changes its transmitting power depending on current requirements. If high data bit rates are necessary, the UE has to increase its transmitting power. This, on the other hand, may result in decrease of transmitting power of other UEs as the summarized transmitting power of all UEs must be always kept below a predefined threshold. Similarly, if less amount of data needs to be sent by the UE, this particular UE can decrease its power to save radio resources in uplink.

## Evolution of HSUPA

Similarly as in case of HSDPA, the HSUPA performance can be further improved by similar techniques as those contemplated for HSDPA. The most notable improvement is achieved by utilization of MIMO technique doubling maximal theoretical data bit rates approximately up to 11.5 Mbps.

The combination of HSDPA together with HSUPA technique is mostly labelled as HSPA that simply refers to high speed data access in both transmission directions. In addition, more recent HSDPA/HSUPA based on Release 7 is often referred to as HSPA+.