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Technology Comparison - StreamStar4 vs. CDMA / EVDO


Quick Comparison
Alloyant StreamStar4
Smart Antenna Systems
8-Element Beamforming
Airlink Technology
Spatial Interference Nulling
Flexible TDD
Cell Breathing Problem
Narrowband + Broadband
Net Spectral Efficiency
0.8 b/s/Hz
2.8 b/s/Hz


CDMA/EVDO vs. StreamStar4 on Range and Efficiency


CDMA and EVDO systems have inherent issues that drastically reduce cell coverage and capacity.

  1. Inefficient single antenna systems
    CDMA employs traditional single base station antennas. Those simple, "old-style" sector antennas simply broadcast the signal across their coverage pattern, regardless of where the actual user is located. This reduces cell coverage and wastes RF power.

  2. Cell breathing
    A notorious CDMA issue, cell breathing occurs when number of active users in a cell grows. As typical with data traffic, active subscribers use much more resources than voice that CDMA and its predecessors were designed for. Cell breathing is essentially intracell interference between active users, which seriously reduces the coverage of the cell.

  3. Inefficient FDD
    CDMA was originally designed for voice, not for broadband data - just like GSM. That is why it uses FDD (Frequency Division Duplex) which uses two separate frequency channels - one for uplink, and one for downlink. However, broadband Internet traffic is heavily downstream-based. This results in a congested downlink and wasted uplink capacity.



The StreamStar4 broadband wireless system uses a smart antenna system (digital beamforming) and a Hybrid Air Interface. This gives multiple advantages:

  1. Higher range: the smart antenna system employs adaptive beamforming on both downlink and uplink, adding as much as 18 dB gain to the link budget.

  2. Higher throughput: the extra beamforming gain allows the system to run higher modulation levels such as 16 and 64 QAM, both on uplink and downlink, increasing throughput.

  3. Higher system efficiency: the smart antenna system enables interference nulling and Dynamic Channel Allocation, which highly reduces co-channel interference (even when running N=1 reuse). This allows tight deployment of multiple StreamStar4 base stations without fear of intercell interference.

  4. The Hybrid SCDMA + OFDMA airlink does not have the "Cell Breathing" effect that pure CDMA does.



Pure CDMA, such as one employed in EVDO systems, suffers from the notorious cell breathing effect, which will significantly reduce overall network range and capacity. Lack of smart antenna systems in CDMA systems means that inter-cell and inter-user interference levels will be much higher, while range and modulation efficiency will be lower, sacrificing performance.

Thanks to hybrid OFDMA + SCDMA, smart antenna technology, Dynamic Channel Allocation and flexible TDD, StreamStar4 will be much more efficient than CDMA especially in dense deployment scenarios. The abundant link budget will ensure that StreamStar4 always performs at high modulation levels, maximizing terminal and base station throughput.


CDMA/EVDO vs. StreamStar4 on Base Station Capacity


EVDO base stations use a 1.25 MHz carrier, and can theoretically deliver 3.1 Mbps per carrier. This will be significantly affected by the same issues as CDMA, such as cell breathing, various internal interference sources, etc.

The net downlink throughput achieved in practical scenarios is about 1 Mbps. This gives EVDO a raw spectral efficiency of 2.48 bits sec/Hz and a net spectral efficiency of 0.8 bits sec/Hz on the downlink. Since EVDO is FDD, a yet another 1.25 MHz channel is used for the uplink, which has an even poorer raw data rate of 1.8 Mbps, which practically achieves 800 kbps net throughput. This is insufficient for data-intensive applications and broadband services.



StreamStar4 Base Stations use a 5 MHz carrier and TDD for duplexing, so both uplink and downlink can achieve those data rates based on the flexible TDD partitioning (there are 7 available U/D partitioning modes).

The net data rate that can be achieved is 15 mbps, leading to a spectral efficiency of 3 bits sec/Hz. This is more than double the EVDO spectral efficiency. The sophisticated smart antenna systems, hybrid airlink, frequency planning, and adaptive modulation ensure that a much higher SNR can be achieved, less intra-cell interference occurs, and terminals achieve higher modulation modes. Thanks to those technologies, the net throughputs per 5 MHz carrier are as high as 13 Mbps.



To truly compare apples to apples: If we compare throughput in the same 5 MHz chunk of radio spectrum, EVDO would deliver 3.6 mbps combined. However, EVDO uplink is seriously low and would most likely be a bottleneck, seriously reducing the number of subscribers that can be served with EVDO, not even considering the CDMA cell breathing and other issues mentioned above. Those would seriously limit the number of carriers that can be co-located for expansion.

StreamStar4 delivers 13 mbps uplink and downlink throughput using 5 MHz. N=1 frequency planning support provided by the smart antenna systems means that base stations can be stacked almost indefinitely, serving much more data per subscriber, much more active subscribers, and eventually a much higher total system capacity.


CDMA/EVDO vs. StreamStar4 on Terminal Throughput


EVDO terminals are theoretically capable of up to 153 kbps uplink and 2 Mbps downlink, depending on the DRC (Digital Rate Control) index, which is essentially the modulation mode and coding rate. However, due to effects such as cell breathing, low spectral efficiency, and BTS loading, the throughputs practically achieved rarely exceed 150 kbps on the downlink, which is the most important factor for data services. EVDO requires a significantly high SNR to achieve 153 kbps rates or more.



SS4 systems have a full suite of terminals with different throughputs of up to 3 Mbps, and a 10 Mbps version is possible. Therefore, the system can support almost all kinds of wireless access applications ranging from low-bandwidth data and voice applications to high bandwidth video applications. All terminals are 64QAM capable on both uplink and downlink for maximum efficiency.



StreamStar4 user terminals are capable of orders of magnitude more uplink and downlink bandwidth than EVDO terminals.