LTE introduces a number of innovations that, in aggregate, continue to push ever closer to the theoretical maximum data rates defined by Shannon’s Law. Advances in multi-antenna techniques, OFDMA methods, wider bandwidth, and protocol efficiencies are fundamental to deliver the promise of 4G Mass Market Wireless Broadband. The amazingly high data rates and sector throughputs (capacity) per cell are fundamental to supplying the ever increasing demand for wireless broadband.
LTE can be deployed in clear spectrum with bandwidth as wide as 20 MHz of paired spectrum (20MHz UL, 20 MHz DL). The high bandwidth of a single carrier radio will deliver unmatched economies when compared with multi-radio legacy approaches, and provides scope for significantly higher capacity compared to 3G-3.5G technologies camped to 5MHZ or smaller spectrum bandwidth.
Sector Data Peak Rate
The recognized sector data peak rate for LTE are as per the below table (Table 1a) depending on the frequency spectrum bandwidth used. It is important to notice that this theoretical maximum does not account for error rate coding, without which in a real life environment, much of the bits will have to be sent several times reducing spectral efficiency to a low level. In consequence, if you take into account a reasonable 5/6 error rate coding, you reach a peak data rate (Table 1b) that is more realistic for field deployment.
Table 1a. LTE Peak Data Rates (Mbps) – No Error Rate Coding
Table 1b. LTE Peak Data Rates (Mbps) – 5/6 Error Rate Coding
Sector throughput
While peak data-rates are important, the essential figure that defines the typical user experience, and more importantly network capacity(deployment cost & OPEX), is average sector throughput. In other words, on average, how much data rate can be realistically achieved in serving all subscribers in a typical sector. Figure 2 compares the average sector throughput capacity of various cellular radio technologies.
Figure 3. Sector Throughput (Capacity)
As we can see in the above figure, LTE provide a significant improvement in throughput capacity at any bandwidth compared to legacy technologies. These capacity improvements are a key to achieving efficiencies necessary to reach the mass market and lower cost per bit achieved by LTE.
The difference in sector throughput achieved by LTE is achieved thanks to the following technical improvements:
- Multiple antenna techniques to increase overall data rate.
- Better multi-path signal handling capability than CDMA technologies.
- No intra-cell interference, as the sub-carriers are for a single user in a time slot.
- Enhanced Interference cancellation is better for reduced inter-cell interference.
- Mitigation of the cell shrinkage vs. loading phenomena of CDMA technologies.
- More efficient Multicast, Broadcast.
- Lowered and more efficient control overhead.
- Frequency Selective scheduling for additional flexibility and efficiency.
User Peak and Expected Average Rate
Expected user data rate is very hard to evaluate and will depend on many factors typical of radio technologies (distance to cell, cell loading, subscriber speed, indoor, outdoor, macro layer or hotspot…).
LTE is quite capable of meeting network requirements for a multi-megabit user experience at the edge of cell even on a macro layer, and effectively delivering wireless broadband to rural markets.
Also thanks to MIMO, Smart antennas, users are likely to have a more consistent experience in comparison to the 3-3.5G experience.
In an indoor environment or “hot spot” areas with dedicated coverage, via pico- and femto-cells, users can expect to reach speed near to the peak rates above.
Latency
In addition to increased data rates, the latency enhancement is likely to provide a noticeable improvement in the user experience. With 3.5G networks, a user can expect a 2 second or longer delay to set up the first connection, and then a 50 ms latency (one way) afterwards. LTE being all IP and having a much flatter architecture, the initial data packet connection should be much faster, typically 50 ms, and then 5 ms latency (one way) afterwards.
What this means, that after pressing buttons on the browser or media player, the user will perceive the LTE network as being very responsive, almost seeming instantaneous like a fixed line broadband connection. This will have a significant impact on user experience and satisfaction, especially when browsing, using netmeeting, streaming rich media, etc… and will enable applications that previously could only be delivered with wired broadband, such as online gaming.
With improvement in both data rate and latency front, it is expected that applications on LTE will provide a user experience very similar to that experienced at home with the wired broadband network providing the true realization of a broadband services that goes anywhere you go.