This section describes the hardware part of the product which details the information about the PCB , the internal antenna  as well as the integration part  

Version 

current Version: v83 (06.11.19)

General Information

Description

The USB Connect LPWA is a USB-Device for cellular machine type communication and supports the cellular 3GPP LPWA-standards NB-IoT and CAT-M1 (LPWA - Low Power Wide Area)

The device is connected to the host device by a USB interface, which supplies the USB-Device with power and transmit and receive data.

The radio signals are transmitted and received by an internal or external antenna via a TS9 connector (external antenna is not included).

The status is indicated by LED:

• RED: Device is powered on
• GREEN: device is registered to the network
• GREEN/RED alternating: device is registered to the network and roaming (this will be the usual pattern)

Remark: The LED can be configured differently with a different GPIO configuration of the  ublox R410 Module via AT-commands (see AT Comand cook book)

      Figure 1: USB connect LPWA Device

      Figure 2: USB connect LPWA Device Bottom view / Top view                                                            

Physical Dimensions

         Figure 3: Physical Dimension                 

Length x Width x Height = (85,75 +/-0,3) x 28,0 +/-0,2) x (11,4 +/- 0,2) mm

Weight: 35 g

IP Rating: IP40 (protected against Solid particles >1 mm, no Liquid ingress protection)

Printed Circuit Board

 Figure 4: General USB layout

External Interfaces

The device has two interfaces:

• USB-A (male)
• TS9 RF-interface for external antenna

USB

The USB connector provides power and data-interface with host devices (e.g. Laptop, Raspberry Pi, SBC, ...).

The connection is specified as defined by the USB standard.

 Figure 5: USB-A connector (male)

Table 1: USB PIN Description

External Antenna Connector (RF)

In order to connect an external antenna, the device has an TS9 connector (female).

Figure 6: TS9 (female) external antenna connector

(Inside RF-Signal, Outside GND)

Examples for recommended external antennas:

• Model, Link
• ...

Supported Frequency Bands

Following LTE-Frequencies are supported.

Table 2: LTE Frequency Bands

Internal Antenna Characteristics

Transmission Characteristic  (Uplink)

Total Radiated Power (TRP) is a measure of how much power is radiated by an antenna when the antenna is connected to an actual radio (or transmitter). TRP is an active measurement, in that a powered transmitter is used to transmit through the antenna. The total received power is calculated and summed up over all possible angles (hence, it is a spherical or 3d measurement) and the result is the Total Radiated Power.

Reception Characteristic  (Downlink)

Total Isotropic Sensitivity (TIS) is a commonly quoted specification in the mobile phone industry. This sensitivity on the antenna and the receiver that make up the communication link. The sensitivity of a receiver is the smallest amount of power that can be input to the receiver, such that the receiver can still maintain reliable communication. This means that data can be transmitted reliably as long as the Block Error Rate (BLER) is 2.0%. To determine this sensitivity, a known data signal is input to the receiver, and the BLER is recorded. The first data signal typically has a high power, to ensure that the BLER is lower than the threshold BLER. The power on the data signal is gradually dropped until the BLER reaches the threshold. (QPSK and a Subcarrier Spacing of 180kHz 12 Subcarrier)

TRP & TIS are parameters directly related to the antenna radiation efficiency, and are well proven measurements in reverberation chambers. The TRP and TIS measurements in a reverberation chamber are standardized and included in the 3GPP Test Specification TS 34.114. 

Table 3 describes the working bands in LTE NB-IOT and LTE -Cat M1 that the USB connect LPWA supports. 

Table 3: NB-IoT Antenna Performance

Table 4:  Cat-M1 Antenna Performance

Integration USB Connect LPWA

Peripheral Layouts

For optimal antenna performance we recommend the use of the layouts detailed in the following figures. To avoid poor antenna performance an incorrect layout is also illustrated.

Recommended layout for low frequency bands  (5, 8, 12, 13, 20, 28)

     Lmin >2 cm: The minimum distance between the dongle and the PCB

• The USB dongle is connected to a PCB min 10 cm* 10 cm (L*W)
  
• Ensure that the dongle is not covered by any metal shielding (such as an earpiece or loudspeaker) unless recommended by the layout.
• Optimum performance can only be achieved if any surrounding metal has a min distance of 2 cm to the dongle.
• Maintain a distance between any other auxiliary devices and the dongle to avoid RF coupling.
• Critical RF exposing device components such as a crystal oscillator and switched-mode power supply must be filtered or shielded to minimize potential impact on the dongle.
• Do not place any components that interfere with antenna performance above the dongle's antenna to avoid a drop in antenna gain.
• The USB dongle is embedded in the longer edge of the PCB, therefore the internal antenna for lower frequency bands is not blocked by the PCB.

 Recommended layout for high frequency bands (2,3,4)

The USB dongle is embedded in the longer edge of the PCB, therefore the internal antenna for higher frequency bands is not blocked by the PCB.

Not recommended layout         

This set-up affects both internal antennas and therefore cannot achieve the optimum performance. For such conditions the use of an external antenna is recommended. If that is no option than the minimum gap of  Lmin >2 cm between the dongle an PCB must be ensured.                                                                       

 Working and Storage Environment 

Table 5: Environmental Conditions

Current Consumption

The IoT module has 3 distinct operating modes with different current consumption.

Deep-Sleep 

The RF section and the application interfaces are temporarily disabled and switched off. The module is temporarily not ready to communicate with an external device by means of the application interfaces as configured to reduce the current consumption.

Active

Module is switched on with application interfaces enabled or not suspended. The module is ready to communicate with an external device by means of the application interfaces unless power saving configuration is enabled.The module is prepared to accept data signals from an external device.

Connected

RF Tx/Rx data connection is in progress.The module is prepared to accept data signals from an external device.

Table 6: Module Current Consumption 

RF Noise Considerations

For optimum performance of the device some RF-constraints need to be considered.

Noise from the Processor Board:

The processor board which the USB Connect LPWA is connected to may emit RF noise signals which results from the clocks of the processor as well as the data rate of digital interfaces such as USB. This RF noise may be received by the internal antenna of the USB Connect LPWA and therefore may limit your receive sensitivity. This may lead to a considerable lower RX-sensitivity in the down link. Therefore the following is recommended:

• Ensure proper EMC-shielding of the processor board.
• Use an external antenna placed outside the RF-noise area to improve RX-performance.

Noise from an active USB-Connection:

The USB-connection is a high speed data interface with a clock, which might also cause interfering RF-noise. The USB 2.0 clock noise shows up at multiples of 480 MHz since the USB clock is 48 MHz * 10 = 480 MBit/s. This type of RF-noise is quite commonly seen at 480/960 MHz on USB powered wireless devices. This might affect performance of the USB Connect LPWA in the lower frequency bands.

Therefore the following is recommended:

• Avoid long USB-Cables between the processor board and the device.
• Ensure proper EMC-shielding of the USB-Connection.
  
• Use an external antenna placed outside the RF-noise area to improve RX-performance.