Multi-DUT PXI cuts small cell manufacturing cost

Base stations are becoming an increasingly high-volume product due to the rise in small cell deployments. As a result, challenges such as reducing the cost of test and maximizing test throughput are becoming increasingly important in device manufacturing. Multi-DUT testing can provide great cost and throughput benefits. This article talks about the major aspects of setting up multi-DUT test systems and also discusses the advantages of the PXI modular platform to implement such systems.

Small cells: High-volume production demands low test cost
As the adoption and usage of smart phones continues to rise, mobile network operators see the demand for data rate and coverage growing – exponentially (figure 1). Cisco's Visual Networking Index estimates that from 2013 to 2018 there will be an 11-fold increase in global mobile data traffic. A view commonly held in the industry is that by 2020 operators must improve mobile network capacity 1000-fold, compared to the beginning of the decade to meet market demands.

Smalls cells are a critical technology in addressing the challenge of delivering higher network capacity. Their coverage area is much smaller than that of traditional "macro cells" (couple of 100 meters versus several kilometers). Small cell base stations operate at lower transmission power, have a smaller size and cost less than macro base stations. However, mobile operators will install – and vendors must manufacture – them in much larger numbers than their bigger counterparts (figure 2).

A number of engineering challenges arise from testing small cell base stations in a high-volume manufacturing environment – and one of the largest concerns is the cost of test.

A big factor in lowering test cost is to increase test throughput. Increase in throughput improves overall production output – and one of the most basic ways to improve throughput is to use high-speed test equipment. Another important factor test engineers should consider is how much their test equipment is utilized.

Utilize your equipment
One of the most important first steps in optimizing a manufacturing line is to better utilize test equipment. In typical manufacturing test of traditional base stations, expensive components such as spectrum analyzers, vector signal analyzers and generators frequently sit idle for long periods of the time. One of the first steps to maximizing test equipment utilization is to use advanced test executives such as TestStand to implement optimized test procedures that allow pipelined, quasi-parallel testing of multiple devices. To fully appreciate the importance of this approach, let us first have a look at the steps taken in typical manufacturing test and then consider specific aspects of multi-DUT testing in more detail.

Anatomy of a typical manufacturing test
Each produced base station goes through a series of manufacturing test steps that characterize and verify the device (figure 3). First, the test stand operator loads the unit into a fixture, where the device boots, and may perform a self-test or load firmware. The next step is to calibrate the RF frontends. Then, typical RF transmitter and receiver tests verify items such as delivered output power, frequency error and linearity against specified limits to produce a pass or fail verdict.