Wireless How To

Introduction

After spending the past year or so with our octoScope-based wireless testbed, I was ready to listen when octoScope suggested upgrading.

The V1 testbed uses octoBox 26" wide chambers, which have proved to be a bit too tight, especially as the size of routers have grown. The desired 8" distance between router under test and the chamber antennas has not been achieved on more than one occasion.

Enter the 38" wide octoBox Stackable anechoic chamber. It measures 24" x 38.35" x 31.2" vs. 18" x 26.35" x 25.2" for the 26" octoBox. The photo below shows the new stack, with a new 38" wide octoBox MPE (Multi Path Emulator) sandwiched between the upper and lower chambers. The key features of the new configuration are described in the octoScope video below.

The Stack

The new stack includes octoScope's new quadAtten programmable attenuator module, which replaces the multiple Vaunix Lab Brick attenuators in the old setup. Dual-shielded cables are also used externally, providing better shielding for test environments with a lot of RF activity. The stack sits on a sturdy base with honkin' big casters that provide very easy rolling. That's an APC Back-UPS 550 and TRENDnet TEG-S80g Gigabit switch sitting on the base in the photo.

Everything runs off the UPS so that power glitches don't interrupt testing. The TRENDnet switch connects the two testbed computers to the SNB LAN and each other. RealVNC is used to remotely access the two testbed computers.

SmallNetBuilder Wireless Testbed V2

Note that the new testbed can handle four RF paths vs. three in the old testbed. This will let us test the new crop of 4x4 AC2350 routers, like ASUS' RT-AC87 that has been available for just about a week as I write this. The 38" octoBoxes are much roomier inside as the photo below shows.

SmallNetBuilder Wireless Testbed V2 inside

Everything is connected as shown in the diagram below. As is our standard, the new process uses Ixia's IxChariot to generate traffic and measure throughput.

octoBox based WLAN Testbed block diagram

Computers

The V2 testbed has gotten a computer upgrade, too. The Dell Optiplex 790 Small Form Factor (Core i5-2400 @ 3.1 GHz) formerly used in the lower chamber now connects to the upper chamber and runs the IxChariot console and the IxChariot test endpoint for the Device Under Test (DUT). The Test STA computer is also a Dell Optiplex SFF machine, but a 9010 model with Core i5 3570 CPU @ 3.4 GHz. After a briefly wrestling with Windows 8 quirks, I decided to stay with Windows 7 Pro on both systems.

Both computers have a TP-LINK TG-3468 PCIe Gigabit Ethernet adapter (Realtek RTL8168B based) installed to provide a second port. This adapter replaces the aging Intel CT's in the V1 testbed that were starting to become unreliable. One port connects to the SNB LAN for control, the other to the DUT or reference STA for test data.