The need for smaller, faster, and more portable devices is persistent in the digital world. The computing power that once required a room-sized machine can now be found in laptops and handheld devices, and you can put stacks of CDs in your pocket in the form of a portable media player. The same trends affect the cellular market and pose some interesting engineering challenges.

Cellular Long Term Evolution (LTE) is the next step forward in cellular 3G services. Some call it 4G. With an expected market rollout in the 2009 timeframe, LTE technology is based on the Third Generation Partnership Project (3GPP) standard that provides for a downlink speed of up to 100 Mbits/s and an uplink speed of up to 50 Mbits/s (Figure 1).

With multiple antennas, speeds can reach more than 320 Mbits/s on the downlink. Fixed wireless and wired standards are already approaching or achieving 100 Mbits/s or faster, and LTE is a way for cellular communications to operate at that high data rate.

For consumers: better, faster, pocket-sized multimedia

High-speed data over cellular networks will enable a rich suite of multimedia services. Cell phones and handheld devices are the new media centers, with access to music, photos, games, video, and a host of connectivity options. Emerging cellular standards such as High Speed Packet Access (HSPA) are already enabling multicall capabilities on handsets and IP Multimedia Subsystem (IMS) services such as push-to-share and multiplayer gaming.

Just like the Internet, the larger and faster your “pipe,” the faster you can access data. For example, downloading a 1-Mbyte song on a slower network can take several minutes. But with a 10-Mbit/s connection, you can download that song in one second. Fast transmission speeds become even more important for emerging services such as broadcast.

Typically, a broadcast channel requires about 300 kbits/s to send streaming or multicast transmissions of compressed video. This means that in 5 MHz, or 5 Mbits of bandwidth, you can broadcast about 16 channels. With 10 Mbits, you can broadcast 32 channels—in real time.

LTE should provide several technical enhancements that will improve the market for services such as Voice over Internet Protocol (VoIP) and videoconferencing. High downlink rates will be important for two-way bandwidth-intensive communications such as videoconferencing. Network latency will also improve, from as much as 200 ms today to 5 to 10 ms with LTE. Latency is a key network metric for enabling services that involve voice, which is very sensitive to transmission delays.

For network operators: flexibility, efficiency and cost savings

LTE will bring many technical benefits to cellular networks. Bandwidth will be scalable, from 1.25 to 20 MHz. This will suit the needs of different network operators that have different bandwidth allocations and allow operators to provide different services based on spectrum. Also, this provides a flexibility that is not available in today’s cellular networks.

Because LTE is a 3GPP standard, an upgrade path is laid out for operators who already use WCDMA networks. Some network operators already can upgrade to the HSDPA standard with little capital expense, depending on the age of their equipment. When new LTE systems are introduced, carriers will use the exact same sites as today’s basestations, because real estate for basestations is difficult and expensive to obtain and because carriers need to maintain their existing coverage patterns. Standards-based upgrades will allow carriers to keep their existing cell tower sites.

3G networks are more spectrally efficient than 2G, and 4G LTE is expected to increase that efficiency. With greater spectral efficiency, operators can serve more standard voice customers and provide more data and services in a given bandwidth. That efficiency could also help carriers improve their average revenue per user or per unit (ARPU), helping to offset the cost of new LTE-capable devices and network upgrades. LTE spectral efficiency is expected to be between three and four times that of HSDPA.

LTE will also migrate cellular networks completely to IP, or packet-based data. Today we have a very complex network that contains a lot of intelligence, which makes the network more expensive. Re-distributing that intelligence from the core of the network toward the end points, i.e., end devices such as cell phones, can make a network much simpler. This in turn can help to reduce the capital expense of telecom network equipment.