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Fig. 1: The license-free ISM band is used by WLAN and Bluetooth, in addition to other radio services. The lower band lies very close to LTE band 40 and the upper is adjacent to LTE band 7. Physically distancing the transmitter from the receiver, i.e. decoupling the antennas, is not practicable because the lack of space is at the root of the problem in the first place. The usual RF shielding methods are likewise not sufficient to resolve the problem. On the other hand, it is possible to use additional bandpass filters on the transmit antennas for WLAN and Bluetooth in order to reduce RF leakage into the at-risk LTE bands. The transmit powers of the individual applications can be reduced as a result of the limited space, thus also reducing any possible unwanted emissions. In the case of noncellular standards, this can be implemented on an individual basis. This is not an option for cellular standards, however, because the transmit power is controlled by the base station. The essential difference between WLAN and Bluetooth – besides the range – is that WLAN uses fixed frequencies while Bluetooth employs frequency hopping. The Bluetooth signal switches randomly between 40 possible channels in a 2 MHz grid (BT4.0) up to 1600 times per second. This prevents the Fig. 2: In spectrogram mode, the individual frequency hops of a Bluetooth signal can be easily viewed and followed. signal from permanently affecting a fixed WLAN signal in the 2.4 GHz band. The reception quality within the vehicle can be further improved both in the frequency and in the time domain. The highly integrated computer chips found in today’s infotainment systems incorporate the various standards. The frequencies to be used for the various applications are already known in the baseband of this chip. This means that a “black list” can be defined for the Bluetooth signal’s frequency hops, listing the channels that could be impaired by an LTE signal and therefore should be avoided. This process is known as adaptive frequency hopping. To prevent impairment of GNSS signals by LTE, it makes sense to employ early detection of data transmis- Smart electronic solutions – from design to finished products Cicor is a leading international high-tech industrial group active in advanced microelectronics, substrates and electronic solutions. The group offers complete outsourcing services and a broad range of innovative technologies, electronics and a wide range of production options from PCB assembly, system assembly, box-building, toolmaking and plastic injection molding. With 11 production sites and more than 20 representative offices worldwide, the group supplies high-quality custom-made solutions to its clients worldwide. cicor.com Europe Advanced Microelectronics & Substrates T +41 32 843 05 00 info-europe@cicor.com Electronic Solutions T +41 71 913 73 73 info-europe@cicor.com America Cicor Americas Ltd. T +1 617 576 2005 info-americas@cicor.com Asia Cicor Asia Pte Ltd. T +65 6546 16 60 info-asia@cicor.com Head office T +41 43 811 44 05 info@cicor.com www.electronics-eetimes.com Electronic Engineering Times Europe November 2015 27


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